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high-pressure
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This report has been reviewed by the U.S. Environmental Protection Agency and
approved for publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection Agency, nor
does mention of commercial products constitute endorsement or recommenda-
tion for use by the U.S. Government.
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high-pressure
compaction 6r baling
of solid waste
final report on a solid waste management demonstration grant
Chapter I of this report (SW-32d) was prepared by the National Bureau of Standards and
the Office of Solid Waste Management Programs, with the cooperation of the American
Public Works Association. Chapters II through V, on work performed under solid waste
management demonstration grant no. D01-UI-00170 to the American Public Works
Association, were prepared by KARL W. WOLF and CHRISTINE H. SOSNOVSKY and
are reproduced as received from the grantee.
Environmental Protection Agency
Library, IL-~Ion '•'
1 North Waolcor Drive
Chicago, Illinois 60606
U.S. ENVIRONMENTAL PROTECTION AGENCY
1972
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ENVIRONMENTAL PROTECTION AGENCY
An environmental protection publication
in the solid waste management series (SW-32d).
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price $1.75
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FOREWORD
Some 75 years ago, American humorist and social
critic Mark Twain described an industrial city on the
Mississippi as a "soot-blackened town." A little more
than a decade later, Theodore Roosevelt admonished
the Nation in a message to Congress not "...to waste,
to destroy, our natural resources, to skin and exhaust
the land...." Today, Twain could add that his
"monstrous big river" is umber-colored with the
wastes it carries, and Roosevelt could look out on
landscape that is defaced and often spoiled by the
wastes deposited on it.
In the intervening years of unprecedented national
growth, reflected in increased population, expanding
municipalities, and greater industrial and commercial
opportunities, we have responded with nonconcern to
a concurrent physical deterioration of the United
States. The first comprehensive water pollution con-
trol legislation was not enacted until 1956; the first
comprehensive air pollution legislation, in 1963.
Finally, less than six years ago, legislation acknowl-
edged a national solid waste problem-a pollution
that can pervade the air, water, and land.
Under the Solid Waste Disposal Act of 1965 (Title
II, PL 89-272) and now under the broader mandate
of the Resource Recovery Act of 1970 (PL 91-512),
municipalities and other nonprofit agencies are eligi-
ble to apply for Federal demonstration grants to
study, test, and demonstrate techniques which ad-
vance the state of the art in the solid waste
management field.
Some disquieting statistics compiled by the Office
of Solid Waste Management Programs point up the
significance of these demonstration projects. The
Nation's annual outlay for getting rid of its debris is
$4.5 billion—and growing. Most of this is expended
for collecting only 180 million tons of the 360
million tons of household, commercial, and industrial
waste actually generated and disposing of it through
predominantly unsatisfactory landfill or incinerator
operations. Ninety-four percent of land disposal
operations consist of open burning dumps that add to
air pollution, or contaminate ground water and
contribute to water pollution—or both; 75 percent of
the incinerators burning municipal waste lack accept-
able air pollution control equipment.
This publication reports on a study and investiga-
tion of an integral process in an alternative transport
and disposal system that, potentially, could alleviate
waste disposal problems encountered in large metro-
politan areas.
SAMUEL HALE, JR.
Deputy Assistant Administrator
for Solid Waste Management
in
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PREFACE
In grappling with solid waste management problems
that worsen daily, public officials in many major
cities, unable to find sufficient land within trucking
distance, are considering using the railroad to carry
solid waste materials to outlying strip mines or other
spoiled lands. There, sanitary landfill techniques
could provide for a successful solid waste disposal
project as well as a construction project to reclaim
the lands.
To promote economical transportation costs, effi-
cient handling, and longer sanitary landfill life,
compacting the collected wastes into tight, dense
bales that stay intact over long distances may be an
advisable intermediate step. Additionally, and quite
important, compaction and baling techniques may
provide the refinement needed to assure that neither
environmental health nor public sensitivities will be
assaulted, and engender the cooperation between the
urban and rural areas which most experts realize will
be essential in the long-term solution of solid waste
problems.
By the year 2000, population in the United States
is projected to double. Most of the increase is
expected to collect in already sprawling metropolitan
areas and their suburban satellites. Even now, in
terms of amounts of wastes generated and spatial
concentration, big cities are troubled most by the
disposal problem. A sanitation official in Chicago—
the site of this compaction and baling study-
interviewed in the Wall Street Journal indicated that,
with nearly all of the accessible open acreage around
the city already consumed, city planners are scram-
bling to identify acceptable alternatives to the present
system which involves incineration and nearby land
disposal sites. Change the name and Chicago could be
any one of numerous metropolises across the Nation
who may have to look to amenable outlying locali-
ties for sanitary landfill sites.
Because the baling-rail haul concept offers one
solution to urban solid waste transport-disposal prob-
lems, this Office has financially supported a rail-haul
feasibility study, being conducted by APWA, and this
complementary compacting and baling study carried
out by the City of Chicago. Not enough is known
about the actual methods, the hazards, possible
causes of failure and economics of the rail haul
concept. The type of railroad cars, the kind of
equipment to be used, the presses, the kind of
binding, the stability of the final product, its weight
and volume, the behavior of the waste before and
after compaction, its density and volume reduction—
these are only some of the questions that were
considered in this study.
James J. McDonough served as the Project Direc-
tor for the City of Chicago while R. Kent Anderson
served as the Project Officer for the Division of
Demonstration Operations.
We hope this report on initial experiments on
compacting and baling of residential solid waste
materials will afford some basic insights into this
relatively recent innovation in solid waste processing.
JOHN T. TALTY, Director
Division of Demonstration Operations
Office of Solid Waste Management Programs
IV
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ACKNOWLEDGMENT
To develop the findings presented in this report
required the cooperation of many people. First and
foremost, recognition is given to the Director of the
project, James J. McDonough, Commissioner, Depart-
ment of Streets and Sanitation, City of Chicago, and
to Deputy Commissioner Theodore C. Eppig. It
would have been impossible to carry out a project of
so complex a nature without their unfailing guidance,
support and encouragement.
Furthermore, recognition is given to James V.
Fitzpatrick, the predecessor of Commissioner
McDonough, who was responsible for the inaugura-
tion and the initial planning and development of this
project.
Acknowledgment is made to the research assist-
ance provided by: Professor V. J. McDonald, Univer-
sity of Illinois, Urbana, Illinois; L. A. Finlayson and
C. K. Cole, IIT Research Institute, Chicago, Illinois;
Edward A. Janulionis, D and J Press Co., Inc., North
Tonawanda, New York; George J. Hartman, Parrel
Corporation, Metals Press Division, Rochester, New
York; Joseph F. Majers, Acme Products Division,
Interlake Steel Corporation, Chicago, Illinois; The
Technical Center, Perm Central Railroad, Cleveland,
Ohio. The contributions made by these persons,
personnel of the City's Department of Streets and
Sanitation, Department of Public Works, and Depart-
ment of Public Health, members of the APWA Staff,
and the many other people who have worked on the
project are deeply appreciated. Furthermore many
persons reviewed the drafts of the report with great
care. Their comments have been invaluable in the
finalization of the report.
Finally, special acknowledgment is due Dr. Karl W.
Wolf and Dr. Christine H. Sosnovsky—the principal
investigators for the project and authors of this
report.
SAMUEL S. BAXTER, Chairman
American Public Works Association
Research Foundation
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CONTENTS
CHAPTER I. INTRODUCTION, SUMMARY, AND CONCLUSIONS 1
CHAPTER II. THE BASIC FRAMEWORK OF THE PROJECT 11
Section One. Project background 11
Section Two. Project objectives 11
Section Three. Guidelines underlying the project execution 12
I. The framework for the basic study approach, 12
II. Process performance parameters of high-pressure compaction in terms
of solid waste rail haul, 12
1. Process performance requirements in terms of material input, 12
2. Process performance requirements in terms of material throughput, 13
3. Process performance requirements in terms of material output, 14
a. Material density, 14
b. Form and shape of the output, 16
c. Size of the bales, 17
d. Stability of the bales, 18
4. Process performance requirements in terms of public health and
environmental control, 19
5. Process performance requirements in terms of cost, 19
III. Implications of process performance requirements for the selection of the
research press, 19
1. Selection of the basic type of compaction equipment, 19
2. Selection of the compaction equipment by speed of pressure
application, 20
3. Selection of the compaction equipment by size, 20
a. Dimensions of the compaction chamber, 20
b. Volume reduction potential, 23
IV. Summary of the operational guidelines underlying the execution of this
project, 23
CHAPTER III. THE HIGH-PRESSURE COMPACTION OF SOLID WASTE
MATERIALS 25
Section One. Experimental setup, procedure, and measurement development 25
I. Experimental setup and procedure, 25
1. Compaction press, 25
2. Press operation, 27
3. Measurement of press parameters, 27
4. Calibration of the deflection and pressure measuring system, 28
vii
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II. Development of methods for the measurement of forces at the bale-
press interface and within the bale, 28
1. Measurements within the bale, 29
2. Measurements of forces at the press chamber walls, 29
3. Chamber wall measurements using penetration gages, 32
Section Two. Description of the solid wastes used in the study 33
I. Residential refuse, 33
1. Composition and moisture content ot loose, sacked, and shredded
residential wastes, 33
a. Composition of winter and spring refuse, 33
b. Moisture content of loose and sacked residential refuse, 34
c. Moisture content of shredded residential wastes, 34
2. Densities of loose, sacked, and shredded residential wastes, 36
3. Composition, moisture content, and densities of oversized wastes, 37
II. Synthetic samples of residential wastes, 37
1. Synthetic residential waste mixtures, 37
a. Composition, 37
b. Moisture content, 37
c. Densities, 39
2. Synthetic samples of paper and water, 39
a. Composition, 39
b. Absorbed moisture in papers, 39
3. Synthetic samples of papers and adhesive, 4i
4. Selected samples containing one or several known refuse components, 41
Section Three. Compaction of refuse 41
I. Procedure, 41
II. Compaction of residential wastes, 43
1. Residential refuse—loose, 43
a. Volume reduction during compaction, 43
b. Effect of incoming densities on volume reduction, 44
c. Changes in volume and bale formation during final compaction, 46
d. Effect of springback forces and pressure holding time on bale
volume during compaction, 47
e. Bale densities during high-pressure compaction, 48
f. Weight losses during compaction, 51
g. Properties of leachings released during compaction, 51
h. Volume expansion of bales after compaction, 53
i. Densities of bales after volume expansion, 55
j. Effect of pressure holding time and moisture content on the
stability of bales after compaction, 56
2. Paper-sacked and plastic-sacked residential wastes, 57
a. Volume reduction during compaction, 58
b. Bale densities during compaction, 58
c. Volume expansion and bale densities after compaction, 58
d. Effect of adhesives on volume reduction ratio and bale densities
during and after compaction, 58
e. Effect of pressure holding time and refuse properties on the
stability of bales of sacked refuse, 59
3. Shredded residential wastes, 59
a. Volume reduction during compaction, 59
b. Bale densities during high-pressure compaction, 60
c. Volume expansion of bales and bale densities after compaction, 60
vm
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d. Effect of pressure, moisture content, and pressure holding time on
bale stability, 62
4. Gas development in residential waste bales, 62
III. Compaction of synthetic refuse samples, 64
1. Synthetic refuse mixtures—loose, 64
a. Effect of pressure on bale volume during compaction, 64
b. Effect of pressure holding time on bale volume during compaction, 64
c. Volume expansion of bales after compaction, 64
2. Synthetic mixtures in paper sacks, 67
a. Effect of pressure and pressure holding time on bale volume
during compaction, 68
b. Volume expansion and bale stability of paper-sacked synthetic
refuse, 68
3. Synthetic paper-water samples: moisture experiments, 69
a. Effect of moisture on bale volume during compaction, 70
b. Volume expansion after compaction as a function of moisture
content, 71
c. Stability of different paper-water samples, 71
4. Synthetic samples of papers and adhesives, 72
5. Compaction properties of selected refuse components, 73
6. Measurements of load distribution during compaction of synthetic
mixtures and other refuse samples, 73
CHAPTER IV. THE STABILITY OF SOLID WASTE BALES IN TERMS OF
RAIL-HAUL SYSTEMS 87
Section One. Basic stability factors and concepts 87
Section Two. Stability test considerations 87
I. Bale stability in terms of rail transport, 87
1. Longitudinal shock and vibration, 87
2. Lateral shock and vibration, 89
3. Vertical shock and vibration, 89
4. Travel distance and time, 90
II. Bale stability in terms of material handling, 90
HI. Bale stability in terms of bale storage and shelf life, 90
IV. Test selection with respect to bale stability required for solid waste rail-
haul systems, 91
Section Three. Vibration and impact tests made under laboratory-scale
conditions involving 12 bales with widely varying characteristics 91
I. Test setup, 91
1. Test equipment and basic test procedure, 91
2. Bale sample, 92
II. Test results, 93
III. Conclusions, 93
Section Four. First 700-mile rail test shipment involving 40 bales with selected
characteristics 104
I. Test setup, 104
1. Rail equipment; transport distance, and route, 104
2. Bale sample, 104
3. Loading configuration, 105
II. Test execution and results, 105
III. Conclusions, 110
ix
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Section Five. Second 700-mile rail test shipment involving 264 bales with
selected characteristics 119
I. Test setup, 119
1. Rail equipment, transport distance, and route, 119
2. Bale sample, 119
3. Loading configuration, 119
II. Test execution and results, 119
III. Conclusions, 123
Section Six. Drop test series covering, in 18 tests, 46 bales with varying
characteristics 128
Section Seven. Observation of bale properties during the numerous bale-handling
operations required at the test site 128
Section Eight. Major conclusions on the stability of compacted solid waste bales 128
CHAPTER V. THE IMPLICATIONS OF APPLYING HIGH-PRESSURE
COMPACTION TO SOLID WASTES FOR RAIL HAUL AND SOLID
WASTE DISPOSAL 135
Section One. Development of compaction equipment performance specifications 135
I. Guidelines for the investigation of alternate comnaction equipment
specifications, 135
II. Press capacity considerations, 136
1. Press productivity and bale size, material density, rate of bale pro-
duction, 136
2. Effects of pressure hold time on production, 136
3. Options concerning bale size and compaction rates in terms of
varying production requirements per 8-hour shift, 138
1. Press capacity in terms of transfer stations for rail haul, 140
a. 50 tons per 8-hour shift capacity, 140
b. 100 tons per 8-hour shift capacity, 142
c. 250 tons per 8-hour shift capacity, 142
d. 500 tons per 8-hour shift capacity, 142
5. Conclusions, 142
III. Hydraulic pressure considerations, 142
1. Availability of hydraulic components and parts, 142
2. Relationship between diameter of hydraulic cylinder and variations
in pressure applied, 143
3. Utilization of hydraulic forces in compaction of solid wastes, 143
IV. Press design considerations concerning press loading, the charging
box, and the geometric shape of the compaction chamber, 145
1. Loading of the press, 146
2. Charging box, 146
3. Geometric shape of the compaction chamber, 147
V. Press design considerations concerning the press frame, 147
1. Press frame in terms of solid waste compaction, 147
2. Basic considerations for a minimum-weight frame, 148
3. Description of an existing single-axis lightweight press frame
(IITRI), 148
4. Application of the lightweight frame concept to multiple-axis
compacting, 149
5. Effects of compaction chamber dimensions on the press frame, 150
6. Operational life of the press frame, 152
VI. Considerations on press foundations, 153
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Section Two. Selected compaction equipment performance specifications 154
Section Three. Prices and construction cost estimates for hydraulic presses
potentially suitable for the high-pressure compaction of solid wastes 155
I. Data limitations, 155
II. Prices and cost of existing hydraulic presses, 156
III. Cost estimates for a lightweight-frame solid waste compaction press, 156
Section Four. Implications of the high-pressure compaction of solid wastes with
respect to rail haul 160
I. Overall public health and environmental control aspects, 160
II. Implications with respect to transfer stations, 160
1. Foundations, 160
2. Pretreatment of the solid waste input materials, 160
3. Press loading equipment, 160
4. Handling of the bales, 161
5. Storage of bales, 161
6. Public health and environmental control, 161
7. Cost, 161
III. Implications with respect to rail transport, 161
1. Bale loading configurations, 161
2. Rail car design, 161
3. Transport operations, distance, and routing, 162
IV. Implications with respect to sanitary landfills, 162
1. Basic construction of sanitary landfills for the disposal of solid waste
bales, 162
2. Operations of landfills for solid waste bales, 162
3. Public health and environmental control measures, 162
V. Conclusions, 163
Section Five. Outlook 163
XI
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INDEX TO TABLES
Table Title Page
1 Conversion of Transfer Station Throughput into Compaction Process Throughput,
Expressed in Tons per Minute and Assuming Variations in the Actual Working Time
As Well As Selected Levels of Productivity and/or Press Utilization 13
2 Range of Purchase Prices for Standard Rail Freight Cars by Load Carrying Capacity 14
3 Approximate Material Density Alternatives Given by the Dimensions of
Selected 100 Ton Standard Rail Freight Cars 17
4 Approximate Patterns for Various Bale Sizes as Suggested by Rail Freight
Car Loading Constraints 18
5 The Weight of Solid-Waste Bales in Terms of 360 Minutes Effective Press Operations,
Varying Overall Throughput Requirements, and Variations in the Number of Bales
Produced per Minute 21
6 Bale Volumes Corresponding to Variations in Selected Bale Dimensions Derived from
Rail Car Loading Dimensions 21
7 Calculated Density Patterns Expressed in Pounds Per Cubic Foot and Based
Upon Variations in Bale Volume and Bale Weight as Suggested by Solid-Waste
Rail-Haul Operating Parameters 22
8 Compaction Chamber-Bale Volumes Based on Various Amounts of Springback 23
9 Composition of Dry Winter Refuse 33
10 Composition of Spring Cleaning Refuse 34
11 Moisture in Residential Refuse 35
12 Moisture in Shredded Residential Refuse 35
13 Densities of Residential Refuse 36
14 Effect of Moisture on the Densities 36
15 Composition of Synthetic Refuse Mixtures (1) and (2) 38
16 Composition of Synthetic Paper Mixtures 39
17 Moisture in Papers 40
18 Volume Reduction Ratios During Compaction of Residential Refuse—Loose
Compacted at about 3500 psi 44
19 Volume Reduction Ratios of Different Bales Compacted at Different Pressures 45
20 Volume Reduction Ratios of Loose Household Refuse as a Function of Incoming
Densities and Compaction Pressures 45
21 Densities of Bales of Residential Refuse, as a Function of Incoming Densities and
Compaction Pressures 50
22 Volume of Bales Compacted at 3000 to 3500 psi for Loads of 200 Pounds Loose Refuse . . 51
Xll
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Index to Tables (Continued)
23 Chemical Analysis of Leachings 52
24 Microbiological Analysis of Leachings 54
25 Volume Expansion of Bales after Compaction 55
26 Densities of Bales after Volume Expansion 56
27 Volume Reduction Ratios of Paper- and Plastic-Sacked Residential Wastes
During Compaction 57
28 Densities of Bales of Paper- and Plastic-Sacked Refuse During Compaction 57
29 Volume Reduction Ratios and Bale Densities of Paper-Sacked Residential Wastes
During and After Compaction 58
30 Effect of Adhesives on Bale Densities and Volume Reduction Ratios for Paper-Sacked
Household Refuse Compacted at Different Pressures 59
31 Volume Reduction Ratios of Different Samples of Shredded Refuse 60
32 Densities of Bales of Shredded Refuse During Compaction 61
33 Volume Reduction Ratios and Bale Densities of Shredded Refuse
During and After Compaction 61
34 Volume Increase of Compacted Shredded Refuse with Time 62
35 Gas Analysis and Bale Temperature of Compacted Spring Cleaning Residential Wastes . . . . 63
36 Average Volume Reduction Ratios of Synthetic Refuse Mixtures 65
37 Volume Increase of Paper-Sacked Synthetic Refuse Bales after
Compaction at Low Pressures 69
38 Typical Distribution of Impacts Occurring in & Railroad Classification Yard 88
39 Probability of Impact Occurrence in Sequential Switching Yards 89
40 ConburTest 92
41 Selected Information on the Twelve Bales Used for the Vibration and
Impact Tests Under Laboratory-Scale Conditions 94
42 Summary of Results from the Vibration and Impact Test Series Conducted
Under Lab oratory-Scale Conditions 95, 96
43 Composition of Bale Sample for First Rail Test Shipment 105
44 Incidences of Longitudinal Impacts on Test Car During Transport of Bales from
Chicago to Cleveland in First Rail Test Shipment 110
45 Summary of Selected Information on the 264 Bales Subjected to the Second
Rail Transport Test Covering a Travel Distance of More than 700 Miles 120
46 Weight of Bales Shipped in the Second Rail Transport Test 121
47 Incidence of Longitudinal Impacts on Test Car During Transport of Bales from
Chicago to Cleveland in Second Rail Test Shipment 121
48 Selection of Local Climatological Data for Chicago, Illinois and Cleveland, Ohio
For the Time Period April 28 to May 15, 1969 123
49 Summary of Drop Test Results 130,131
50 Matrix of Press Capacity Alternatives Based on an Effective Production Time of
480 Minutes per 8-Hour Shift and on Variations in Overall Throughput, Size and
Weight of Bale and Pressure Holding Time 139
Xlll
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Index to Tables (Continued)
51 Matrix of Press Capacity Alternatives Based on an Effective Production
Time of 360 Minutes per 8-Hour Shift and on Variations in Overall Throughput,
Size and Weight of Bale and Pressure Holding Time 141
52 Variations in the Total End-Frame Load-Bearing Requirements Resulting from
Changes in the Length of the Compaction Chamber at a Load of 2000 psi
Applied to the End-Frame and a Constant Chamber Volume 152
53 Summary of Economic Data on Hydraulic Presses Potentially Suitable for the
Compaction of Solid Wastes 157
54 Estimated Lightweight Frame Weights for Single- and Double-Axis Solid-Waste
Compactors, Based on Different Bale Sizes, Two Types of End Section Construction,
A Cubic Configuration of the Bale in the Compaction Chamber, and an 18:1 Volume
Reduction Ratio 158
55 Cost Estimates for Lightweight Solid-Waste Hydraulic Compaction Presses
Based on Variations in Bale Sizes, End Sections, Ratios of Frame Weight to
Total Weight, Number of Compaction Stages, and Material Cost 159
xiv
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INDEX TO FIGURES
Figures Title Page
1 Compaction Rates for Various Levels of Productivity 15
2 Correlation Between Increase in Car Purchase Cost and Increase in
Car Length for 100-Ton Box, Gondola and Flat Cars 16
3 Compaction Press 26
4 Electronic Measuring System Diagram 27
5 Penetrometer Gage 29
6 Strain Gaged Liner Plate 30
7 Response of Strain Gage to Loads from Various Materials 31
8 Penetration Gage Calibration Curve 32
9 Residential Wastes—Loose. Ram Deflection During High-Pressure Compaction 44
10 Volume-Pressure Relationship for High and Low Density Refuse 47
11 Residential Waste, Sequence of Ram Deflection for Loose Refuse Compacted
Initially Up to 3500 psi (a) and then at 1150 psi (b, c, d) 49
12 Residential Wastes. Effect of Pressure Holding Time on Bale Height 49
13 Average Densities of Residential Wastes During and After Compaction 56
14 Synthetic Refuse-Loose. Decrease in Bale Height as a Function of Pressure 65
15 Decrease in Bale Height as a Function of Holding Time 66
16 Synthetic Refuse-Loose. Average Volume Increase of Both Mixtures With and
Without Holding of Pressure 67
17 Synthetic Refuse-Loose. Volume Changes of Bales Compacted for 5 to 10 Minutes 68
18 Paper-Sacked Synthetic Refuse-Decrease in Bale Height During Compaction
With and Without Holding of Pressure 69
19 Effect of Moisture Content on Bale Height During Compaction of Paper Samples
Compacted at About 3500 psi 70
20 Increase in Density as a Function of Moisture Content 71
21 Volume Expansion of Compacted Paper Bales Containing 10 to 50 Weight
Percent of Added Water 72
22 Total Load Distribution at Bottom and Top of Bales 74
23 Sample of Impact Register Chart Showing the Interpretation Standards 194
24 Illustration of the Bale Loading Configuration Used in the First
Rail Test Shipment 106, 107
25 Example of Impact Recordings Made During the First Rail Test Shipment 108,109
26 Record of Air Temperature in the Test Car During the Second
Rail Test Shipment 122
27 The Interrelationship of Waste Compaction Tonnage and Compaction
Rate for Various Bale Weights at Approximately 1 Ton Per Cubic Yard Density 137
xv
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Index to Figures (Continued)
28 The Influence of Pressure Hold Time on the Production Rate 138
29 Interrelationship Betwee'n Diameter of Hydraulic Cylinder, Hydraulic
Pressure, and Pressure Applied for Two Sizes of Bales in the
Compaction Chamber 144
30 Approximate Relationship Between Volume Reduction and Pressure Applied
for Maximum 2,000 and 3,000 psi Applied Pressure Systems 145
31 Concept of the Geometry of the IITRI Lightweight Press Frame 149
32 Configuration of the Compaction Chamber 150
33 Selected Interrelationship Between Length of Compaction Chamber and the
End Load Restraining Forces Required for Chamber Volume of Eight Cubic Feet 151
xvi
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INDEX TO PHOTOGRAPHS
Compaction of Solid Wastes 76
Compaction of Loose and Paper-Sacked Residential Wastes 77
Individual Bales Compacted at About 3500 psi 78
Compacted Winter Refuse-Loose and Paper-Sacked 79
Bales Compacted at About 2000 psi 80
Bales, Various 81, 82, 83, 84
Compacted Bales After Handling and Relatively Long Term
Exposure to Weather Conditions 85
Test No. 1 97
Test No. 2 98
Test No. 3 99
Test No. 4 100
Test No. 5 101
Test No. 6 102
Test No. 7 103
Boxcar Used for Rail Test Shipment Ill
Bales Loaded with Sand Bags 112
Bracing of Bales Before Shipment 113,114
Condition of Load After Return to Chicago 115,116,117
Bales on Truck After Unloading 118
Bales Before Second Test 124
Condition of Load After Return to Chicago 125,126,127
Tests No. 9 and No. 8 132
Tests No. 10 and 12 132
Tests No. 13 and No. 11 133
461-084 O - 72 - 2 XVU
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CHAPTER I
INTRODUCTION, SUMMARY, AND CONCLUSIONS
1. INTRODUCTION
This report documents some initial experiments in
this country on the high-pressure compaction of
municipally collected solid wastes. The American
Public Works Association (APWA) Research Founda-
tion performed the work for the City of Chicago
under a Federal demonstration grant from the Bureau
of Solid Waste Management (BSWM*), of the Depart-
ment of Health, Education, and Welfare (HEW).
The BSWM prepared this introductory chapter
jointly with the Technical Analysis Division and
Product Evaluation Technology Division of the Na-
tional Bureau of Standards. The remainder of the
report (Chapters II through V) is reprinted as written
for the City of Chicago by the APWA Research
Foundation.
The compaction and baling study is an outgrowth
of another demonstration grant project conducted by
the APWA for HEW and many local government
jurisdictions in the United States and Canada. This
demonstration grant studied the potential benefits of
rail haul in solid waste disposal systems.** A short
series of spot tests performed during the rail-haul
study had indicated that the high-pressure compac-
tion of municipal solid wastes was feasible and could
contribute substantially to the concept of the rail-
haul of solid wastes away from the urban environ-
ment. These preliminary tests also showed, however,
that additional testing was needed to: (1) expand the
preliminary test results; (2) investigate more thor-
oughly significant parameters in the high-pressure
compaction of solid wastes; (3) determine the opera-
tional implications of this promising approach to
solid waste processing.
With the help of APWA, the City of Chicago
prepared and submitted an application for a three-
phase grant to BSWM which proposed that:
"The ultimate objective of this project is to
determine the optimum requirements for the
design of suitable production -scale equipment
to compress solid wastes into high-density
economical payloads for transport by rail and
to test the operational aspects of such a
system."
*Now the Office of Solid Waste Management Programs of the
U.S. Environmental Protection Agency (EPA).
**Demonstration Grant No. G06-EC-00073, "Investigate the
Potential Benefits of Rail-Haul as an Integral Part of Waste
Disposal Systems."
The main objective of the first phase, reported on
here, was:
"...to obtain (production-scale) information on
the various parameters which affect the com-
paction of refuse into bales readily handleable
after compaction."
The first year's program was to be designed:
"...to provide reliable information to permit the
development of performance specifications for
production-scale compaction (equipment). This
would involve the use of an experimental press
equipped with a number of interchangeable
parts so that the effects of various press
variables on the compaction of refuse of differ-
ent characteristics can be determined."
Eighteen secondary objectives were listed:
"...to dimension the advantages and disadvan-
tages of various bale sizes with respect to
compression and/or baling;
...to determine the number and positioning of
the strokes needed to produce suitable bales;
...to investigate alternatives which would reduce
the stroke requirements while enhancing the
baling; e.g., the utilization of pressure- or
spring-controlled counter-pressure plates; time
and throughput are of considerable concern
since rail-haul deals with operations typical for
mass production.
...to ascertain the feasibility, parameters, and
operating requirements of extrusion;
...to measure the influence of variations in the
pressure applied in general and within the
framework of varying «trnk<> arrangements:
...to analyze the impact of production cycle
times and of the speed of compression;
...to investigate the production and handling
parameters of varying bale configurations;
...to determine the workability of production-
scale operations concerning bales of exact
volume, exact weight, or exact density;
...to establish design criteria for the feeding
devices needed;
...to evaluate the stability of bales of different
sizes and configurations;
...to ascertain the influence and behavior of
selected types of refuse and refuse composi-
tions under various pressures applied and within
the framework of bale and press variations;
...to develop workable solutions for solving the
moisture problem;
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...to investigate the possibilities of achieving
public health and total environmental control
safeguards for the rail-haul system through the
compression or associated operations;
...to arrange for the necessary biological and
chemical bale sample analysis with appropriate
departments of the U.S. Public Health Service;
...to specify the fail-safe provisions needed for
full-scale operations;
...to calculate the techno-economic parameters
resulting from varying approaches to produc-
tion-scale operations,
...identify the instrumentation and controls
needed for full-scale operations; and,
...to establish design criteria and performance
specifications which can be released to various
equipment manufacturers in order to foster
competition and enlist the industrial develop-
ment capabilities for the benefit of the rail-haul
systems."
From the outset, the program—an ambitious
undertaking—encountered difficulties, particularly in
obtaining an experimental press with interchangeable
parts. Finally, a 17-year-old, three-stroke metal scrap
baler, donated by General Motors Corporation, was
modified and installed in a Solid Waste Research
Facility built by the City of Chicago. In practice, the
only press variables that could be studied were
applied pressure in one direction (after a gathering of
the load by the machine into a volume with fixed
rectangular cross-section perpendicular to the direc-
tion of applied pressure) and the length of time the
pressure was held. Only one configuration and rough-
ly one size range of bale was possible (16 inches by
20 inches by variable 14 to 18 inches), in the form of
a rectangular parallelepiped.
In Section 2, a fairly elaborate summary of the
report is given. This includes only the major results.
2. SUMMARY OF THE REPORT
Chapter II (pages 11-24) is entitled, "The Basic
Framework of the Project." The first two sections
discuss the project background and project objectives.
This is followed by the development of guidelines by
APWA for the execution of this investigation. This is
an attempt to take into account the comprehensive
objectives of the project in light of the tight
constraints of manpower, time, and funds. In devel-
oping these guidelines, consideration was given to
process performance requirements in terms of materi-
al input, throughput, and output. For the latter, there
are discussions relating to the output density (pp.
14-15) form, shape, size, and stability of the bales
produced (pp. 16-19); requirements in terms of cost,
public health, and environmental control (p. 19) are
also discussed briefly. Funding and time limitations
eliminated the possibility of building a compaction
device specifically designed for this research project.
The implications of these process performance re-
quirements of input, throughput, and output were
then taken into consideration in seeking a press for
the research project (pp. 19-23). Details of the actual
press used are given in Chapter III (p. 25). The
operational guidelines developed by APWA are given
on pages 23 and 24 of the report and are also
reproduced here:
1. Confine the compression tests to residential
solid waste mixtures and their components.
2. Base the process developments on material
throughput or capacity ratings of 0.14 to 1.4
tons per minute.
3. Try to achieve average material shipment den-
sities of at least 50 pounds per cubic foot.
4. Avoid the investigation of very low or very high
pressure applications, if they do not relate to
the volume reduction or stability requirements
of this project
5. Give priority to the development of square or
rectangular bales. Consider other configurations
only in case of need.
6. Limit the developments to a maximum of four
ultimate bale sizes—one of their sides being
1.12, 1.50, 2.25 or 3.00 feet. If necessary,
concentrate the research efforts on the 1.50-
and 2.25-foot bale.
7. Determine carefully the amount and, in partic-
ular, any directional orientation of springback
occurring in the bales after exit from the press.
8. Develop bales which are stable for 9 days and
suitable for rail transport of up to 150 miles
within this time period.
9. Emphasize the application of pressure for
achieving bale stability. Investigate other stabil-
ity aids only in case of need.
10. Check for pollution caused by the compaction
process itself. Engage in pollution control re-
search if compaction by itself causes any form
of pollution which cannot be handled in an
acceptable manner by existing control methods.
11. Orient all investigations toward the estab-
lishment of a compaction process of minimum
cost. Investigate specifically avenues of possible
equipment development which promise cost
reductions and thereby will foster a more
widespread application of the high-pressure
compaction process.
12. Obtain a hydraulic press which:
(a) is capable of applying relevant pressures
upwards of 2,500 pounds per square inch
within a time span of less than 30 seconds to
solid waste materials in an enclosed chamber;
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(b) has dimensions of its compaction chamber
which can support an extrapolation of the test
results to compaction chamber dimensions
ranging from a minimum of 1.68 to 8.54 cubic
feet to a maximum of 0.70 to 20.25 cubic feet;
(c) provides an in-press volume reduction
potential of at least 15.1.
Attention is called to the fact that these guidelines
determine the scope as well as the depth of the
project's total result. The press used also provided
constraints upon the project which conditions some
of the results. It was not possible to dimension the
effects of these constraints in this initial effort; this
research aspect is recommended for inclusion in any
follow-up project (p. 24).
Note should be taken that since the press was out
of order for one week, there was an actual testing
time of only nine weeks (p. 11).
Chapter III (pp. 25-85) is entitled, "The High
Pressure Compaction of Solid Waste Materials." The
compaction experiments were carried out with a
17-year-old normal metal scrap baler which was
reconditioned and modified. The modifications in-
cluded an increase of the total force of the third ram
and the addition of a series of ram locks to prevent
the movement of the first and second low-pressure
rams and the cover during the final high-pressure
compaction. The first two rams operated in a
horizontal plane and constituted a gathering of the
refuse in the charging box into a rectangular paral-
lelepiped with cross-section dimensions of 16 by 20
inches perpendicular to the vertical. In normal opera-
tion the cover was locked into position and, after
gathering, and initial compaction by the first two
rams, these rams were locked into position. The
high-pressure ram was then operated in the vertical
direction, usually until it reached a predetermined
indicated gauge pressure, and the compaction was
completed. To remove the bale from the press, all
three rams were first moved slightly out of position
to remove the pressure from the bale. After removal
of the cover plate from the top of the box, the third
ram was again activated to eject the finished bale out
of the charging box (pp. 25-39). All of the bales
produced were initially rectangular parallelepipeds
(box shaped) with initial cross-section dimensions of
16 by 20 inches. The height of individual bales varied
but was usually in the range of 14 to 18 inches.
An electronic measuring and recording system was
installed to measure:
(a) ram displacement of the intermediate ram;
(b) hydraulic pressure of the high-pressure ram;
(c) ram displacement of the high-pressure ram.
This system produced time-history records of the
event. Later a second output device was added to
produce a direct plot of the applied pressure versus
the displacement of the third ram. Examples of these
charts, however, are not given in the report (pp.
27-28).
Attempts were made during the study to measure
the forces active in bale formation. This is because a
knowledge of the various forces developed in the
press frame, at the bale interface, and within the bale
are of importance both with respect to press design
and for understanding of the compaction process.
Existing techniques were utilized; but it was found
that standard measuring techniques are not easily
adaptable to refuse compaction and that new meth-
ods will have to be developed. An appreciable amount
of work was done and several approaches were
evaluated. One of the approaches showed great
promise; it utilized penetration gauges for measure-
ment at the interfaces between the chamber walls and
the refuse. Although the application of the penetra-
tion gauge method could not be fully explored, the
results indicate that useful information can be ob-
tained from it. Contour drawings, not shown, were
made of the load levels of the indentations produced
during the compaction in the bottom and top plates.
The total load distribution at the bottom and top of
the bales is shown for different samples and different
compaction conditions. The presented results show
that peak loads can be developed both at the bottom
bale face (resting on the high-pressure ram) and at the
top of the bale. It is pointed out that at present it is
not clear whether the peaking occurs primarily as a
result of individual material properties of the bale
components, or whether it is related to the compac-
tion conditions. Further work in this direction is
indicated (pp. 29-33, 73-75).
Two types of refuse (as delivered by truck),
classified as winter and spring refuse, were examined
in detail as to their contents. The winter refuse was
largely composed of paper products with a range
from about 50 to 80 percent by weight of the total
refuse (p. 34). The refuse received from the City of
Chicago during the spring period contained a large
proportion of yard rakings and dirt, which were
absent in the winter refuse. In addition, the spring
refuse contained more glass, food, and metallic wastes
but appreciably less paper. The composition, densi-
ties, and moisture content of loose and sacked
residential refuse, of shredded (by a Heil-Gondard
shredder) refuse received from Madison, Wisconsin,
and of oversized wastes were also determined. De-
tailed results of these studies are presented in a
tabular form (Tables 9-14, pp. 33-36). The densities
of the incoming uncompacted waste samples ranged
from 3.8 to about 15.9 pounds per cubic foot
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depending primarily on different void proportions in
the mixtures.
Synthetic samples of residential wastes were espe-
cially prepared for this study to test the effect of
single waste components and mixtures on the com-
paction of wastes. Two large mixtures were especially
prepared to simulate the composition of dry house-
hold refuse. Some samples were placed in paper sacks;
others were used in loose state. To simulate overall
liquid content of dry household refuse (as determined
previously with the city-delivered refuse), liquids
were either added separately or introduced through
solid wastes containing bound or absorbed water
(such as vegetables, fruit, and paper). A series of
samples containing only paper products and a known
amount of water was prepared in order to investigate
the effects arising from the interaction of moisture
and papers during and after compaction. In addition,
several series of experiments were carried out to
determine the moisture contained in papers before
the addition of water (pp. 37-41).
A series of compaction experiments, using the
converted three-stroke metal baler, was carried out on
samples of the loose residential refuse, on the
synthetically constructed samples, on synthetic mix-
tures to which adhesives had been added, and on
specially secured refuse components. The pressure
applied by the third ram was varied during individual
compaction runs. The pressure applied by the third
rams included 500, 750, 1000, 1500, 2000, 2500,
3000, and 3500 psi. A few samples were also
compacted at higher pressures, about 6000 psi, by
concentrating the available force of the high pressure
ram on a smaller surface area. The experiments were
exploratory in nature rather than statistically design-
ed. As an example, the number of samples subjected
to a particular indicated pressure, on a particular
holding time of applied pressure, was not set in
advance, but determined day by day from operating
considerations. In some instances experiment levels
(pressure, holding time, type sample) are "one of a
kind." The recording equipment provided records of
the variation of the applied pressure with time as well
as the distance the ram moved during the pressure
application. The time required to compact the bale in
a so-called "normal fast run" was approximately 17
seconds. The decrease in volume was measured during
compaction as a function of applied pressure. Subse-
quently, the expansion in volume of the compacted
bales, outside the compaction chamber, was measured
over a period of time (in some cases for 24 hours and
longer). The densities of the compacted refuse during
and after compaction were determined. The following
are some of the principal results:
1. Changes in volume for samples of loose residen-
tial refuse:
(a) The volume reduction during compaction
of samples of similar density averaged about
13:1 at applied pressures of 3000 to 3500 psi
and decreased systematically to about 9:1 at
about 900 psi (Table 20 and pp. 44-46).
(b) The volume reduction ratio was higher if
the density of the incoming refuse was lower
and vice versa (Table 20, Figure 10, pp. 44-46).
(c) Holding of pressure during compaction
always led to a decrease in bale volume (p. 47).
(d) Increase in pressure or increase in time ot
pressure application led to a decrease in bale
volume during compaction, and to a reduction
in expansion force after compaction (p. 47).
(e) An example (six different refuse samples
prepared from the same load) shows that
holding of pressure for either 5 or 10 minutes
at about 1000, 1500, and 2000 psi led to the
same approximate decrease in bale volume (p.
48 and Figure 12, curve b).
(f) From a series of 8 samples there is indica-
tion that the reduction in volume with time at
low pressures is not of the same magnitude as
that which can be achieved at highest pressures
in fast runs (p. 48 and Figure 12).
2. For all kinds of samples, evaluation of record-
ings of the changes in ram deflection with time
indicated that the maximum decrease was reached
after less than one minute of pressure application
(pp. 48, 64, 67, 68, and Figures 15 and 18).
3. For sacked residential refuse, synthetic loose
refuse, and synthetic paper-sacked refuse the
compacted volume reduction ratios were similar to
those obtained with loose residential wastes of
similar densities (p. 58, p. 64, and Tables 27 and
36).
4. An illustration of the effects of pressure hold-
ing time on bale volume during compaction for
samples from one of the two mixtures of synthetic
loose refuse shows that the decrease in bale height
at about 850 to 1000 to 1500 psi was after
holding of pressure, nearly equivalent to the
decrease which was achieved by compaction in
normal fast runs at a 700 psi higher pressure. At
about 2000 to 2500 psi the decrease with time was
nearly equivalent to that obtained in a fast run at
about 500 psi higher pressure. Increase in pressure
holding time from 5 to 10 minutes had no effect
(p. 64 and Figure 15).
5. The major result with respect to volume and
densities is that variations in the incoming densi-
ties of the different refuse loads had little effect
on the density of the compacted bales. These
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variations, however, did have an appreciable effect
on the volume reduction ratio. As a result, refuse
samples of the same volume produced bales of a
large variety of sizes, whereas samples of the same
weight produced bales of similar sizes. This finding
suggests that control of the weight of the incoming
refuse provides a better means for the controls of
the compacted bale (p. 50).
6. The major results on springback of volume
expansion are:
(a) Springback, or volume expansion, of the
compacted bales starts immediately after the
release of the compaction pressure (p. 53).
(b) Most of the springback takes place within
the first 2 minutes; expansion during that time
amounted to 50 to 60 percent of the original
compacted volume (p. 53).
(c) The springback continues after the first 2
minutes at a slower rate. Bales stored individu-
ally and left to expand without any restriction,
grew up to 95 percent larger than their original
compacted volume (p. 55).
(d) The expansion of normal bales occurred
preferentially, following the sequence of the
three-step compaction process: least expansion
occurred in the direction of the lowest pressure
application, first ram movement; and the max-
imum expansion occurred in the direction of
the highest pressure, third ram movement. This
order of expansion was the same independent
of the solid properties of the compacted refuse
(p. 55).
7. Many observations are made with regard to the
stability and appearance of bales after compaction
(pp. 46, 56, 57, 59, 62, 67, 69, 71, 72, Chapter IV
and p. 146). The principal results for loose
residential waste are:
(a) The major factors found to affect the
stability of compacted bales of loose residential
wastes were compaction pressure, time of pres-
sure application, and the moisture contents of
the wastes (p. 56).
(b) In the absence of excessive moisture, com-
paction at high pressures resulted in the forma-
tion of stable bales. On the other hand, bales
compacted at low pressures were quite fragile
(P- 57).
(c) Fragile bales were usually obtained after
compaction at pressures between about 500
and 1000 psi. These bales occasionally fell apart
immediately after removal from the baler.
Some fell apart after being handled successively
several times. An improvement in stability was
found for bales compacted at pressures between
1000 and 1500 psi. However, the stability of
most bales was markedly improved after corn-
action at 2000 psi and up to 3500 psi. A
further increase in pressure, up to 6000 psi,
produced no apparent improvement in bale
stability (pp. 46, 57).
(d) The overall stability of the bales compacted
at about 1000 and 1500 psi usually improved
appreciably if the force on the bales was held
for several minutes. The bales compacted at
about 1000 psi for 5 minutes seemed to be as
stable as those compacted at 1500 to 1750 psi
without holding of pressure. Similarly, the bales
compacted at about 1500 psi for 5 minutes
appeared to have the stability properties of
samples compacted at about 2000 psi without
holding of pressure (p. 57).
(e) The stability of bales of very high moisture
content was always poor, irrespective of the
compaction pressure applied. There were, how-
ever, indications that the stability of the bales
containing an appreciable amount of moisture
could be improved if the compaction pressure
were lowered (p. 57).
8. The compaction properties of a number of
selected refuse components and mixtures were
investigated. Some of the interesting results are:
(a) Rubber, plastic scrap, and food materials
could not be compacted on their own.
(b) Mixtures of oversized wastes including bed
springs, refrigerators, etc., produced excellent
bales. (For a detailed listing see p. 73).
9. Special experiments were carried out to corre-
late moisture content to paper content, the major
component of refuse mixtures (pp. 39,40, Tables
16 and 17, pp. 69-72, Figures 19 and 20).
Furthermore, papers exhibit pulping and expan-
sion characteristics in the presence of moisture,
and this determines to a large extent the compac-
tion properties of residential waste mixtures. The
major results of these compaction experiments
are:
(a) A small amount of moisture has a beneficial
effect on the compaction of residential wastes
of high paper content (p. 69).
(b) The stability of all paper bales which
contained a very large amount of moisture was
found to be poor (p. 71).
(c) Most compacted bales of paper bundles
were unstable irrespective of the moisture
content (p. 71).
(d) Separated newspapers and paper mixtures,
to which about 35 weight percent of water was
added, were reasonably stable (p. 71).
10. A limited series of experiments (pp. 41,42,
72) was carried out with paper mixtures to test the
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effect of adhesives on bale stability and on the
volume expansion of paper-sacked refuse and
paper bales. The work with adhesives was not
pursued further because the stability of the baled
household refuse was found to be quite good
without the use of adhesives. The major results on
adhesives are:
(a) Volume expansion was not substantially
reduced by the addition of adhesives (p. 72).
(b) The paper bale stability was distinctly
improved by the addition of adhesives, and the
appearance of the bales was excellent (p. 72).
(c) The presence of adhesives sprayed on the
outsides of samples each containing 10 bags of
paper-sacked household refuse immediately be-
fore compaction had no effect on the compac-
tion properties of wastes during compaction
(pp. 58 and 59).
A small effort was expended to perform chemical and
biological analyses of liquid compressed from the
bale. The investigation was limited to a few tests,
which were inadequate to assess the pollution poten-
tial of this liquid (pp. 52-54, Tables 23 and 24. See
also pp. 62 and 63 , Table 35 and pp. 160-163 for
some related discussion on overall public health and
environmental control aspects).
Chapter IV (pp. 87-133) is entitled, "The Stability
of Solid Waste Bales in Terms of Rail-Haul Systems."
For current solid-waste rail-haul systems the bales
should be capable of surviving a rail transport of at
least 150 miles distance and of 3 to 6 hours duration
of movement. During this travel the bales would be
subjected to longitudinal, lateral, and vertical shocks
and vibrations. The bales would be subjected to
handling and possibly dropping at the transfer station
and at the disposal site. Assuming a maximum
24-hour transport time and a once-a-week pickup, it
is necessary that 9-day-old bales be suitably stable for
rail-haul transport and for disposal site operations
(pp. 87-90).
The first series of vibration and impact tests was
carried out under laboratory conditions and involved
bales of widely varying characteristics. Two sets of
bales compacted at gauge pressures of about 2000
and 3500 psi were used. One set of bales was strapped
and a corresponding set not strapped. The results
indicated that all bales were exceedingly stable
regardless of whether they were strapped or not, or
whether they were compacted at the lower or higher
pressures. All the bales exceeded the general stability
specifications developed above. It was apparent that
strapping improves the stability of the bales. Howev-
er, since the unstrapped bales withstood the vibration
and impact tests successfully, it was decided not to
conduct additional strapping tests within the present
project. It was also noted that a bale judged "good"
before testing tended, as a rule, to remain in this
category after testing, and a bale judged "poor" still
survived all the tests in this category (pp. 90-93,
Tables 40,41,42, photographs: pp. 97-103).
Although the first stability tests were indeed
positive, they nevertheless were made on a laboratory
scale and were not fully representative of actual
rail-haul conditions. Thus, two actual rail-haul tests
were made with the car containing the compacted
bales moved by regular freight trains. The transport
distance exceeded 700 miles in each test shipment
being made from Chicago to Cleveland and back and
through three railroad yards. In each test the car was
equipped with an impact recorder. In the second test,
the car was also equipped with a humidity and a
temperature recorder. In the first test, a sample of 40
bales made from regular Chicago household refuse as
it came off the truck, were made up as follows:
paper-sacked, compacted at 2000 and at 3500 psi;
and loose, compacted at 2000 and at 3500 psi. None
of the individual bales or the bale sets were strapped.
None of the bales failed, i.e., broke apart, during the
test. Two second-layer front bales which had fallen
off and been thrown around in the car were only
partially damaged. All the other bales were judged to
be in very good condition, or at the very least, still in
acceptable condition. All bales that were weighted
down by either sand bags or other bales were judged
to be in better condition than the bales not weighted
down. The bales made from refuse in paper sacks
appeared, as a rule, to be in better condition than
bales made from loose refuse. Finally, there was a
relatively small amount of spillage from bales made
from loose refuse. There was no spillage from the
paper-sack bales (pp. 104-110, photographs: pp.
111-118).
The second rail shipment test was set up similar to
the first rail shipment test, except on a greatly
enlarged scale. In this test, a sample of 264 bales was
structured to contain an equal number of bales made
from loose household refuse and from household
refuse placed in paper sacks before compaction at
gauge pressures of 1500, 2000, and 2500 psi. Each
sub-group of samples was set up to include bales 6 to
8 days old at the outset of the test shipment. This
test encountered transport conditions even more
severe than those experienced in the first rail test
shipment. Examination of the car in Cleveland by
members of the Penn Central Railroad research staff
showed that the bulkheads on one end of the car had
collapsed and some bales had spilled into the center
of the car. The bulkheads at the other end of the car
were also damaged. However, all the bales were found
to be in good condition; not one bale had disintegra-
ted. Inspection after the return trip to Chicago
showed that all bales came back intact. The amount
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of spillage was estimated again as less than 1 percent
of the total weight of the bales. Indications are that
the bales produced a significant amount of heat and
moisture, suggesting that some degradation of the
organic constituent of the bales took place (pp.
119-123, photographs: pp. 124-127).
To study the effects of accidental dropping on
bale stability, a series of 18 severe drop tests was
carried out on 46 bales of varying characteristics. The
test results show that solid waste bales which appear
stable after exit from the press, are capable of taking
a considerable beating from drop impacts. This holds
true regardless of whether the bales are dropped
individually or in groups. However, it appears that
bales produced at higher compaction pressures are, as
expected, more resistent to drop impacts than bales
produced at low compaction pressures (p. 128).
Numerous observations on stability were made
during the 10-week test period. These can be sum-
marized as follows:
1. Bales that appear cohesive after exit from
the press can be handled without special pre-
cautions.
2. Bales exhibiting apparently significant struc-
tural defects are still surprisingly strong in
terms of the bale-handling operations per-
formed.
3. Exposure of bales for about 3 weeks to
outside weather conditions during February to
May 1969 did not cause an appreciable amount
of structural deterioration.
4. Spillage, as a rule, amounted to less than 1
percent of the weight of the bale.
Chapter V (pp. 135-163) is entitled, "The Implica-
tions of Applying High Pressure to Solid Wastes for
Rail-Haul and Solid Waste Disposal." The implica-
tions of high-pressure compaction for the solid waste
field are viewed primarily with respect to the develop-
ment of compaction equipment performance specifi-
cations and the implementation of rail-haul systems
(pp.135, 160-162).
Compaction equipment Implications:
1. The development of compaction equipment
performance specifications was made in consid-
eration of selected press design and operation
parameters. The conceptual, technoeconomic
analyses were confined to hydraulic presses (pp.
135-142,154-160).
2. The press capacity analysis was based on one
shift per day and 360 minutes effective opera-
tions per shift. This represents an efficiency
equivalent of 75 percent of an 8-hour shift and
of only 25 percent of a 24-hour per day
capacity (pp. 140,142).
3. In addition, the press capacity analysis takes
into account variations in:
(a) throughput from 50 to 500 tons per
shift;
(b) bale size from 0.25 to 1.0 cubic yard in
the compaction chamber;
(c) rate of bale production from two bales
per minute to one bale per 3 minutes;
(d) the pressure holding time ranging from
15 seconds to 1 minute (pp. 136-142).
4. Within this framework the analyses indicate
a wide application potential for presses with a
bale size of 0.50 or 0.75 cubic yard in the
compaction chamber. The analyses suggest fur-
thermore that transfer stations pegged at more
than 250 tons per shift should have more than
one press (p. 142).
5. The investigations of press hydraulics sug-
gest that 3000 psi in hydraulic and 2000 psi in
applied pressure, and a specified pressure hold-
ing time rather than higher pressures, should be
preferred in the development of compaction
equipment suitable for the rail-haul of solid
wastes (pp. 142-145).
6. The charging box analysis indicates that an
inclusion of over-sized wastes in the input
mixtures does not create difficulties. The same
analysis also suggests that the charging box
cover be designed to perform an active function
in the compaction process (pp. 145 and 146).
7. The press should be charged from the top by
a batch system. In high-volume operations, it
should not require more than 5 seconds to charge
the load at a total cycle interval of 1 minute. The
requirements are much less demanding in low-
volume operations (pp. 146,163).
8. Existing press trame construction techniques
appear to be more than adequate for solid
waste presses. In terms of operational life, the
press frame should be suitable for 2.9 million
load cycles. The high-pressure compaction of
solid waste is not accomplished by impact in
the process under consideration (pp. 147, 148,
153).
9. Press frame considerations suggest that the
bale dimension parallel to the direction of the
final pressure application be as long as possible
within reasonable limits. Additional research on
the transmission of forces through the bale in
the compaction chamber might give guidelines
leading to significant process improvements
(pp. 150-152). [It might show, for example,
that the bale dimension parallel to the direction
of the final pressure application should be as
short as possible in order to obtain a more
uniformly compacted bale.]
10. The analyses of press frame design consid-
erations include relatively new lightweight
-------
frame construction principles. Some of these
principles have been used successfully in
Europe as well as at the IIT Research Institute
in Chicago. They appear to be of advantage for
the high-pressure compaction of solid waste,
especially in multiple-axis compaction systems
(pp. 148-153). [If the compaction press is
simply designed so that the frame of the press
supports or withstands the reaction forces
resulting from the compaction operation, then
it isn't important whether the force is applied
to the horizontal or vertical plane; however,
economics are achieved through minimization
of foundation costs if presses are designed to
compact in the horizontal plane.]
Compaction Equipment Performance Specifica-
tions:
1. The specifications discussed in this report
deal with the functional performance required
from the compaction equipment as a unit. They
do not address themselves to equipment design
needed to perform the task specified (p. 154).
2. The information given throughout this
report indicates that several sets of such press
performance specifications can and should be
developed. The sets of specifications should be
determined primarily by the materials to be
compacted, press design and operation con-
siderations, and local solid waste disposal con-
ditions (pp. 135, 136, 152-154,163).
3. Within the scope of this project, it was only
feasible to develop one example of very general
performance specifications for a solid waste
compaction press. This example reflects the
project findings as developed within given
constraints which include the limitations of the
press used in this project (p. 154).
4. Incorporating most of the major specifica-
tion elements, this example is discussed in
detail in this report. It provides for:
(a) the compaction of residential/
commercial solid wastes in heterogeneous
mixtures which behave like semi-elastics
under compaction;
(b) a press capacity of about 250 tons per 6
hours (75 percent utilization during one
8-hour shift per day) or about 330 tons per
full 8-hour shift;
(c) applied pressure of 2000 psi in the final
compaction stage;
(d) a pressure hold of 15 seconds at 2000
psi;
(e) an overall volume reduction capability
of 18:1;
(f) a total cycle time of 1 minute;
(g) a service life of 2.9 million cycles;
(h) a bale size in the compaction chamber
of 25.7 by 27.7 by variable inches, on the
average 34.0 inches, which was determined
by selected rail-haul requirements (p. 154).
[This report does not provide evidence to
indicate that this example of general perfor-
mance specifications for a solid waste com-
paction press takes into account that a pressure
loss occurs within the bale in the direction of
the applied force. It is also not evident that it
would be reasonable to expect that a stable bale
of this size is possible at an applied pressure of
2000 psi in the final compaction stage.]
5. These press performance specifications as
well as some of the key findings herein pre-
sented are confirmed by reports of solid waste
compaction studies and equipment proposals
submitted by European organizations after the
completion of this project's research efforts.
Compaction Equipment Cost:
1. The compaction equipment cost data pre-
sented in this report include depreciation of the
purchase price and power and maintenance.
They do not include interest and other
financing charges, return on investment, and
personnel. The depreciation is calculated on a
20-year write-off period although the service
life of similar presses has been found to be 10
to 15 years longer (pp. 155-160).
2. An analysis of prices and cost/performance
parameters for existing hydraulic presses, which
in case of need, are suitable for the high-
pressure compaction of solid wastes, indicates
that depreciation and power amount to about
50 cents per ton in 7-hour/5-day-per-week
operations. An additional 7-hour shift would
reduce these costs by about 15 to 25 cents per
ton (p. 156 and Table 53).
3. However, none of the existing presses was
specifically designed for the compaction of
solid wastes; consequently, the cost data reflect
the price of using "substitute" equipment.
Thus, these analyses suggest that the high-
pressure compaction of solid waste might cost,
as reported in the APWA rail-haul interim
report, less than 40 cents per ton including all
major equipment investment and operating
charges but excluding financing costs, labor,
and return on investment (p. 156).
4. A higher press utilization factor than was
used in this analysis could significantly improve
this cost/performance ratio. Cost estimates
made for a lightweight-frame solid waste
compaction press indicate that the basic invest-
ment cost may be reduced substan-
tially-perhaps by as much as 50 to 60 percent
-------
excluding development expenditures. This
would compound the advantages gained by
increasing the utilization of the press (pp. 147,
156,160). [Depending on the number of
presses produced, the development expendi-
tures when taken into consideration may dras-
tically reduce these gains.]
Implications of High-Pressure Compaction Sys-
tem:
1. The implications of high-pressure com-
paction for the rail-haul of solid wastes are
discussed to some extent in this report; how-
ever, there are plans to cover them in more
detail in a separate publication being prepared
on Rail Transport of Solid Wastes, by the
APWA. This report presents only some of the
preliminary findings that could be developed in
connection with work performed during the
compaction test program (pp. 135,160-163).
2. Concerning transfer stations, the rail-haul
link, and the ultimate disposal of the bales by
the sanitary landfill method, the information
shows:
(a) that high-pressure compaction of solid
waste is highly applicable to rail-haul; and,
most important,
(b) that the combination of high-pressure
compaction and rail-haul results in environ-
mental control benefits comparable to those
available in the currently acceptable meth-
ods of processing solid wastes (pp. 160-163).
3. High-pressure compaction of solid wastes
could also increase the utilization of sanitary
landfill space.
3. CONCLUSIONS
1. The application of high-pressure compaction to
solid waste disposal has been examined experi-
mentally and theoretically in quite some detail and
appears to be a process which can be applied on a
production scale with many attendant advantages.
2. It has been demonstrated that stable bales can
be produced by the high-pressure (2000 to 3500
psi applied pressure) compaction of loose and
sacked household refuse; and that these bales can
successfully survive the handling and shocks associ-
ated with comparatively long (up to 700 miles)
rail-haul trips.
3. The results indicate that further investigation is
needed and warranted for the development of
process and equipment improvements and to
establish the technical and economic feasibility of
this basic process as a component of a total solid
waste management system.
4. COMMENTS
This report presents the results of the first phase
of a project which had as an ultimate objective, the
development of "the optimum requirements for the
design of suitable production-scale (compression)
equipment." Further work is required to achieve this
ultimate goal. For example, the project does not
completely answer questions on the impact of
moisture content on bale stability, public health, and
environmental control. Although the work reported
represents exploratory research and a number of the
results are, therefore, indicative rather than defini-
tive, many relevant considerations and observations
are documented. To guide the reader and to encour-
age him to scrutinize the entire report rather than just
this initial chapter, we have summarized each chapter
and pointed up those features to be considered in
reading the text.
One of the general organizational features of this
report is that because of the large amount of
information presented, considerable cross-referencing
might be required by the reader depending upon his
objectives.
It is important to note that the material on
compaction is organized according to results on:
1. Residential refuse—loose (pp. 43-57);
2. Residential refuse—paper-sacked (pp.
57-59);
3. Residential refuse—shredded (pp. 59-63);
4. Synthetic refuse-loose (pp. 64-67);
5. Synthetic refuse-paper-sacked (pp. 67-69);
6. Synthetic refuse-paper and water (pp.
69-72);
7. Synthetic refuse-papers and adhesives (p.
72).
If one is interested, for example, in the effects of
holding times of applied pressure, there are discus-
sions and summaries of the data on the effects of
holding times on residential waste, paper-sacked
waste, and height of bales in the appropriate sections
on pages 46-49, 57, 59-62, 64 and 66-69. Similarly,
the effects of moisture with respect to the type of
wastes used are given on pages 33-41, 56-57,59-62,
64 and 69-72. The reader must keep track of the
heading under which a particular result is discussed.
Also, the reader must refer to the text proper for
qualifying statements that are not always apparent
from a particular table or chart.
The authors of Chapter III have chosen to report
their results in summary form rather than present the
basic data for each individual experiment. Where
several samples have been subjected to the same
treatment, the distribution of results is reported only
in terms of the maximum, minimum, and average
values. Although this presents adequate information
-------
for many readers of the report, results of each
individual test would have been more useful to the
researcher. It is to be noted that a large number of
results are obtained from annotated recording equip-
ment charts which registered the actual applied
pressure and the ram displacement of the high-
pressure ram as functions of time. These recordings
were not made available in the report for further
valuation, The reader should pay special attention to
the fact that in several tables and charts the results of
a single experiment under one set of conditions is
compared to the average results from a large number
of samples under another set of conditions. Chapter
III concludes (pp. 76-85) with a number of pictures
of the compaction process and compacted bales. The
bales are classified by composition, pressure applied,
and time of pressure application. However, informa-
tion has not been provided to indicate the acceptance
of the bales in terms of stability or appearance. In the
application of the results of the compaction experi-
ments to the rail-haul study, the important properties
are the final volume of the compacted bale after
springback and the stability of the bale rather than
the in-press volume reduction ratio.
The reader should take special note that most of
the compaction experiments described in Chapter III
were made with bale sizes which ranged in the
compaction chambers from 14 to 18 inches high, that
an extrapolation is made in Chapter V to a bale size
of 34 inches high to obtain optimum loading of rail
cars. It should also be noted that the configuration of
the press influences the findings to some unknown
degree and that no experiments were conducted on
the larger size bale. Therefore, further research is
needed to establish the stability of bales of the size
recommended for optimum loading.
10
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CHAPTER II
THE BASIC FRAMEWORK OF THE PROJECT
Chapter II identifies the basic framework of this
project in terms of project background, project
objectives, and project execution.
SECTION ONE-PROJECT BACKGROUND
This project was initiated at the end of
November 1967, as a result of findings developed
previously by the Research Foundation of the
American Public Works Association in a study on the
rail-haul of solid wastes. The APWA study is carried
out for the U. S. Department of Health, Education,
and Welfare and many local government jurisdictions
in both the United States and Canada. The rail-haul
study findings suggested:
1. that the high pressure compaction and/or baling
of solid wastes is the most effective and
economical way of processing solid wastes for
large quantity shipments through rail-haul to
remote disposal areas,
2. that solid waste compaction is consequently one
of the most vital rail-haul system development
inputs, particularly for operations designed to
service large metropolitan areas,
3. that a full-or semi-production-scale solid waste
compaction test program would supply the
answer to a critical need and speed up the
implementation of solid-waste rail-haul systems,
and
4. that the results of a solid waste compaction test
program, as envisioned, would benefit not only
rail-haul system developments, but, in addition,
other facets of solid waste disposal as well.
The above findings were derived from
preliminary experiments conducted by the APWA
rail-haul study team in order to ascertain the
feasibility of high pressure compaction for solid
wastes. The information gathered by spot tests and
some of the conclusions drawn are detailed in an
interim report entitled, "Rail Transport of Solid
Wastes-A Feasibility Study," Oqtober 1968. This
report has been published by the U. S. Department of
Health, Education, and Welfare, Public Health
Service, Consumer Protection and Environmental
Health Service and Environmental Control
Administration.
In summary, the spot tests showed conclusively
that the high pressure compaction of solid wastes is
feasible. However, they also showed that additional
testing was needed (a) to substantiate the preliminary
test results, (b) to investigate more thoroughly the
many factors of significance in the high pressure
compaction of solid wastes, and (c) to determine the
operational implications of this new and promising
approach to solid waste processing. It was apparent
that more supporting information was needed for
both government and industry to convert promising
indications into practical technology.
The formal proposal for the compaction project
was filed on January 14, 1968. The project was
approved on March 1, 1968, and funded for a May 1,
1968, starting date. The actual testing began on
January 28, 1969. The interim period was used to
locate and acquire a used press, to recondition as well
as adapt as far as possible that press for the test
purposes, and to erect and equip the test facility
needed.
SECTION TWO-PROJECT OBJECTIVES
Broadly stated, it was the basic objective of this
research project to obtain production-scale
information on the various parameters which affect
the high pressure compaction of solid wastes into
bales that would be readily handleable for rail-haul.
To accomplish this basic objective it was
necessary to pursue a large number of corollary
sub objectives. Within the constraints of effort and
time, the sub objectives required the study team to
investigate many aspects of the high pressure
compaction of solid wastes such as:
1. the influence of selected pressure variables on
compaction and baling,
2. the number and positioning of compression
strokes needed to produce a suitable bale,
3. the effects of variations in the total cycle time as
well as the speed of compression,
4. the advantages and disadvantages of various bale
sizes and configurations,
5. the stability of the bales produced,
6. the implications of varying refuse compositions
with respect to high pressure compaction and
baling,
7. the necessary public health and environmental
control requirements,
8. the techno-economic parameters of
production-scale operations, and
9. the development of compaction equipment
performance criteria to guide and enlist the
research capabilities of industry for the benefit of
11
-------
rail-haul systems, as well as the solid waste
disposal field.
In the over-all, the project objectives were cast in
terms of applied research and thus describe the
project as both exploratory and developmental in
character.
SECTION THREE-GUIDELINES
UNDERLYING THE PROJECT EXECUTION
The project had to be executed within the
framework of several conflicting demands. To be
considered on the one hand were the comprehensive
objectives of the project, the complexity and scope of
the problem, and the stakes ultimately involved. On
the other hand, there were tight constraints of
manpower, time, and funds.
Thus, in contrast to most research projects, this
project had only a minute margin for the always
necessary exploratory and research development
efforts. Hence it was crucial that stringently limiting
guidelines be developed for both the setup and the
execution of all the test and development activities.
I. THE FRAMEWORK FOR
THE BASIC STUDY APPROACH
The framework for the basic study approach was
characterized by significant experimental constraints
and, since the press was out of order for one week,
there was an actual testing time of only nine weeks.
In addition, it was necessary to balance the manifold
project objectives in terms of the professional efforts
available for research.
Consequently, the study approach was structured
to focus primarily on three key project goals even to
the exclusion of other very worthwhile study
subjects. The three goals selected concern:
1. the development of compaction equipment
performance specifications,
2. the development of stable bales suitable for
rail-haul, and
3. the exploration of possibilities for the
development of a minimum-cost solid waste
compaction process.
It must be highlighted in this context that, being
both exploratory and developmental in character, this
project was to take the first major step toward the
application of a promising solid waste disposal
technology. As a result, the basic study approach for
this project had to be comprehensive in scope but
selective in depth. Furthermore, in producing an
initial version of a new technology, the approach had
to be cognizant of further research which could be
aimed at an evolutionary perfection of the basic
process.
Finally, corresponding to the framework for the
basic study approach, the guidelines had to be
relevant to real-life operational requirements.
Specifically .considerations had to be given to:
1. the establishment of process performance
parameters for high pressure compaction in terms
of solid waste-rail-haul, and
2. the selection of the basic type of high pressure
compaction equipment suitable, or at least
acceptable, for the purposes of this research
project.
II. PROCESS PERFORMANCE PARAMETERS OF
HIGH PRESSURE COMPACTION IN TERMS OF
SOLID-WASTE RAIL-HAUL
The main purpose of processing solid wastes for
rail-haul is the improvement in the cost/performance
relationship of the over-all system operations. Since
sol id-waste rail-haul involves primarily material
handling and transport, the processing relates to the
way the materials are made ready for transport and
handling throughout the system.
As a result, the rail-haul-oriented performance
requirements of high pressure compaction must be
determined in terms of material input, throughput,
process output, public health and environmental
control implications, and cost.
1. Process Performance Requirements
In Terms of Material Input
A solid-waste rail-haul system is intended to
handle successfully and economically as great a
variety as possible of the solid waste materials
generated by residents, municipal operations,
commerce, and industry.
These input materials may be characterized as
heterogeneous material mixtures of sometimes widely
varying compositions which, as a rule, behave like
semi-solids under compaction. Specifically, urban
solid waste mixtures might include items such as food
scraps, nylons, textiles, facial tissues, newspapers,
bound and unbound moisture, furniture, glass,
refrigerators and industrial/commercial packaging
materials.
In view of both the great variety and the posbible
combinations of input materials and the critically
short project period, it obviously was not feasible to
consider an all-inclusive test effort. Fortunately,
however, residential wastes are reported to represent
about 50 percent of the total urban solid waste load.
Furthermore, they are also "reported to contain many,
if not most, of the kinds of solid waste materials
discarded by industry and commerce.
Thus, it was decided to use in the compaction
tests mainly residential solid waste mixtures and
components, including oversized wastes.
12
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2. Process Performance Requirements
In Terms of Material Throughput
Transfer stations are needed in virtually all
solid-waste rail-haul systems. They represent the first
building block of the operations and the place where
the compaction process would most likely occur.
To satisfy the demands for various types of
transfer stations, the APWA solid-waste-rail-haul
project is projecting the development of stations
capable of handling 50, 100, 250, 500, 1,000, or
2,000 tons of solid waste per 8-hour shift. To put
these ratings in perspective, it might be stated that a
50-ton transfer station appears suitable for servicing
about 15,000 people, while a 2,000-ton station can
service 500,000 to 600,000 people.
In converting these over-all throughput ratings of
transfer stations into time-related process workloads,
it must, of course, be recognized that an 8-hour shift
does not always imply 480 minutes of actual working
time. Depending upon the degree of automation, the
process might, for example, be shut down for 60
minutes during each shift in order to allow for lunch
and coffee breaks. Furthermore, it is not reasonable
to assume that a station will always operate at peak
efficiency. The implications of variations in the actual
working time as well as the productivity of the
compaction press are summarized in Table 1.
The calculations include time variations from 35
to 100 percent in the utilization of the press, in order
to gauge simultaneously the impact of peak loading
that may result from existing schedules for refuse
collection and delivery.
In analyzing these data it must be recognized that
only a few communities need, at present, transfer
stations capable of handling 1,000 or 2,000 tons of
solid waste materials per 8-hour shift. In addition, the
high cost of collection tends to favor the selection of
multiple transfer stations with a smaller capacity,
even in communities or regions that generate a large
amount of solid waste materials. In the light of these
arguments and the constraints of the project it was
decided to focus the available efforts on
press-throughput ratings below 2 tons per minute.
The implications of this decision are illustrated in
Figure 1. In this figure the transfer station capacity
ratings are plotted against production time as well as
press throughput expressed in tons per minute.
The placement of the curves suggests that, within
the constraints given in Table 1, a l,000-ton/8-hour
shift transfer station should be served by two press
units capable of handling 500 tons per 8-hour shift.
The curves furthermore suggest that, given an
actual working time of only 6 hours per shift, a
maximum press throughput of about 1.4 tons per
minute would be quite acceptable for the same time
conditions. A minimum throughput of 0.14 tons per
TABLE 1
Conversion of Transfer-Station Throughput into Compaction-Process
Throughput, Expressed in Tons per Minute and Assuming Variations
in the Actual Working Time as Well as Selected Levels of
Productivity and/or Press Utilization
Transfer
Station
Throughput
Requi rement
(Tons/8-hr
shift)
50
100
250
500
1000
2000
Compaction Press Throughput
Actual Working T
480 Minutes
Level s
100V
480
Min.
0. 10
0.20
0.52
1 .04
2.08
4.16
of Pres
85V
408
Min.
(all
0.12
0.24
0.61
1 .22
2.45
4.90
s Util iz
50V
240
Min.
data exp
0.20
0.41
1.04
J 2.08
4.16
8.33
at ion
35V
168
Min.
ressed ir
0.29
0.59
1.48
2.97
5.95
11.90
me Per 8-Hour Shift
420 Minutes
Level s
100V
420
Min.
i tons pe
0.11
0.24
0.59
1.19
2.38
4.76
of Pres
85V
357
Min.
r minute
0.14
0.28
0.70
1.40
2.80
5.60
s Util iz
50V
210
Min.
*)
0.24
0.47
1.19
J 2.38
4.76
9.52
at ion
35V
147
Min.
0.34
0.68
1.70
3.40
6.80
13.60
*Data are slightly rounded.
13
-------
minute is indicated.
As a result of these considerations, process
throughputs varying from 0.14 to 1.4 tons per minute
were chosen as the prime concern for this research
program. Thus, the compaction equipment is
presumed to operate at an efficiency rate of 75
percent of the stated capacity.
3. Process Performance Requirements
In Terms of Material Output
The output of the high pressure solid waste
compaction process must be viewed in terms of form
or shape of the materials, the size and stability of the
individual output units, as well as material density.
a) Material Density
For the shipment of goods and materials it is
important to consider both their volume and their
weight. Both the space occupied and the weight to be
carried represent, to varying degrees, cost factors.
The interrelationship between volume and weight
is termed material density. A decrease in the volume
of a given amount of material, while keeping its
weight constant, increases the material density.
Analyses conducted during the APWA
solid-waste-rail-haul study suggest that the density of
the materials shipped has a direct bearing on shipping
cost. Factors such as car deadweight per ton of net
load, utilization of the available freight carrying
capacity, and train configuration represent some of
the major variables. In certain instances, for example,
a doubling of the material density might even reduce
by one-half the number of a given type of cars
needed.
In gauging material density targets for rail-haul
operations, it was found prudent to base the decisions
initially on the carrying capabilitites of the standard
types of rail freight cars presently produced.
Custom-made designs, including high cube cars, are
very expensive, as may be expected; they may cost
two to three times as much as a standard car of
equivalent capacity.
A comparison of the straight purchase price of
rail cars, excluding any financing cost and return on
investment, suggests already in itself that the desired
density targets should be based on the utilization of
the 100-ton car. The purchase prices are roughly as
given in Table 2.
In evaluating the data in Table 2 it must be
TABLE 2
Range of Purchase Prices for Standard Rail Freight Cars
by Load Carrying Capacity
Type and Length of Car
Box Cars
1*0.6 feet
50.6
60.9
Gondola Cars
Low side 3 '6"
52.6 feet
65.6
Flat Cars
50 feet
60
68
89
Load Carrying Capacity
70 tons
(dollars)*
11,500 - 1^,200
13,800 - 15,000
19,000 - 20,700
13,200 - 1A.200
15,700 - 17,300
11,000
15,000
17,250
20,600
100 tons
(dollars)*
12,500 - 15,200
1*4,800 - 16,000
20,000 - 22,200
1A,200 - 15,700
16,700 - 18,800
12,000
16,500
18,250
21,600
Sources: Various railroads and railcir manufacturers.
*The Low values of the purchase price range reflect
volume discounts which are attainable through orders
involving several hundred cars.
14
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recognized that 40-foot-long gondola and flat cars, as
well as cars with load limits of 50 tons, are no longer
considered production-line items. The data show that
the purchase price, as a rule, increases by only $1,000
with an increase in the load carrying capacity from 70
to 100 tons.
Concerning the 100-ton cars, the data in Table 2
also reveal an interesting relationship between
purchase price and length of car. This relationship
shown in Figure 2 on the following page suggests, for
example, that an increase of 20 percent in the length
of a 50-foot box or flat car increases the purchase
price by approximately 40 percent. Thus, from a car
investment point of view, it is evident that compact
cars be given careful consideration in the selection of
desirable material density targets.
For the purposes of this project, the data and
arguments presented thus far appear to be sufficient
to indicate desirable density ranges of solid waste
materials for rail shipment. The full case for the
selection of a given rail freight car is planned to be
made in the final report on the first phase of the
APWA rail-haul project. Obviously, many cost factors
in addition to the purchase price are involved.
The material density alternatives available within
the framework of the above data are calculated by
distributing the net load over the volume of car space.
These calculations take the existing car-loading
requirements and experience into consideration. For
example, loading regulations require that flat cars, as
a rule, be loaded only to a height of approximately 8
feet, if packaged materials of a kind similar to solid
wastes are shipped. Furthermore, experience in the
utilization of box-car space dictates that the
FIGURE 1
Compaction Rates for Various Levels of Productivity
1000
tons/shif tN
2.0 •
c
'i
c
o
I/I
en
c
Q.
-C
O)
o
1_
-C
I-
1/1
0)
1_
Q.
6 hours
/Working time
tons/min
0.28 tons/min
•
0.14 tons/min
100
200
300 kOQ
Production Time (min./shift)
461-084 O - 72
15
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FIGURE 2
Correlation Between Increase in Car Purchase Cost and
Increase in Car Length for 100-ton Box. Gondola, and Flat Cars.
$23,000
$20,000 .
Box Car
$22,200
Box Car-Volume Discount Price
$20,000
Flat Car
$18,250
$15,000
$15,200
$18,800
Gondola Car
12,000
$10,000
_L
40'
50' 52.6'
60'
65.6' 70'
Car Length
Source: Basic data on freight car purchase prices obtained
from various railroads and rail car manufacturers.
theoretically available volume must be reduced by
approximately 20 percent in order to arrive at
realistic volume/weight relationships. Thus, the
calculated density ranges for the materials to be
shipped are shown in Table 3.
In interpreting the foregoing data it should be
understood that the densities indicated represent
minimum densities. These are the densities required if
the net load capacity and the realistically available
space are both to be fully utilized. A decrease in the
density will result in a full utilization of the available
space but an under-utilization of the net-load-carrying
capacity. An increase in the density will result in an
under-utilization of the available space.
As a result of the analyses presented in this part
of the report it was decided to aim, if possible, for
solid-waste-shipment densities averaging at least 50
pounds per cubic foot.
This decision carries significant implications
concerning the application of pressure in terms of
volume reduction and volume expansion after
compaction. Very high pressures, for example, are
not to be investigated for their own sake within the
scope of this project, i.e., if they do not cause an
appreciable increase in the density above 50 pounds
per cubic foot. Conversely, very low pressures are also
to be de-emphasized if they fail to attain the volume
reduction needed and potentially achievable on the
basis of the materials being compressed.
b ) Form and Shape of the Output
To provide maximum flexibility for
solid-waste-rail-haul operations, it is necessary to
consider the application of high pressure to the waste
materials not only with respect to volume reduction
but also with respect to the output form and/or shape
of the product resulting from the compaction
process.
Man has packaged goods and materials
throughout recorded history to improve the
productivity of his material handling efforts. Today
only relatively homogeneous materials are, as a rule,
shipped "loose" because they permit, by their very
16
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homogeneity and if shipped regularly in sufficient
quantities, the utilization of tailor-made and
therefore most efficient material handling methods.
Examples of such materials include grain, cement,
and coal. But even coal is already processed to at least
some degree in order to provide a relatively uniform
unit size for the material handling functions involved.
Thus, if compaction is done at all, then it should
also be used as far as possible to process the highly
heterogeneous materials into a desired form.
Consequently, the compaction of solid wastes might
be considered as a method of packaging or
"containerization". In keeping with current industry
experience, compaction should furthermore aim to
produce a "one-way" containerization. In the ideal
case, the materials to be shipped should provide, by
being processed through compaction, their own
container or packaging.
The specific output form or "packaging" of the
materials must, of course, be determined in terms of
both the utilization 6f space in storage, transport, and
landfill as well as the placement and stacking
requirements of these operations It is known that
specific configurations, such as spheres or hexagonals,
add strength to a package because of their
configuration. Nevertheless, industrial practice
suggests that square or rectangular forms are
preferred. These configurations are more adaptable to
varying handling and storage conditions, particularly
if packages of varying sizes might also be involved.
On the basis of these considerations it was
decided to give, within the scope of this project,
priority to the development of square or rectangular
bales. Correspondingly, other configurations were
only to be investigated if stability requirements and
their implementation would suggest such a course of
action.
c) Size of the Bales
Concerning solid-waste rail-haul, the size of the
bale is primarily determined by the loading
dimensions of freight rail cars. All the other material
handling and transport operations could be adjusted
readily to fit the size of the bale.
The loading dimensions of rail cars can vary
considerably in the length and height of the car, but
they are almost alwavs fixed with respect to the
TABLE 3
Approximate Material Density Alternatives Given by the
Dimensions of Selected 100-Ton Standard Rail-Freight Cars*
Type and
Length of
Car
Box Cars
40.6 feet
50.6
60.9
Gondola Cars
(Low side)
52.6 feet
65.6
Flat Cars
50.0
60.0
68.0
Theoret ica 1
Cubi c
Capaci ty
4000
5000
6000
1780
2220
4700
5640
6390
Pract ica 1
Cubic
Capaci ty
3200
4000
4800
1780
2220
3760
4500
5100
Density per Cubic Foot
of Practical
Cubic Capacity
62.5
50.0
42.0
112.0
90.0
53.0
44.0
39.0
Source: Basic data on freight car purchase cost and dimensions
obtained from various railroads and rail car manufacturers.
*A11 data are slightly rounded.
17
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width of the car. Specifically, the limits of the
loading dimensions of standard freight rail cars are
approximately 9 feet wide, by a maximum height of
8 to 10 feet, by a maximum length of 60 to 70 feet.
These standard car dimensions make it necessary
to size the solid waste bales primarily with respect to
the width and, subsequently, the height of the car.
The length of the car, although an important factor in
car cost, may, for practical purposes, be considered in
this context as a variable factor.
To achieve a maximum utilization of the
potentially available freight car space, the shipping
configuration of the bales should follow any one of
the combinations of dimensions given in Table 4.
The table indicates that a wide variety of bale
sizes are well suited to solid-waste rail-haul. For
example, a bale could be dimensioned 9.0 x 8.0 x
variable, or 9.0 x 4.0 x variable, or 3.0 x 8.0 x
variable, or 3.0 x 4.0 x variable, etc. The data
indicate, however, that at least one dimension of the
bale should approximate 9.0, 4.5, 3.0, 2.25, 1.5,
1.12, or 1.0 feet.
In view of these considerations it becomes highly
important to determine the springback characteristics
of the compacted solid waste mixtures which, as a
rule, contain elastic material components.
Springback, as reported in the interim report on the
APWA rail-haul study, was found to be an important
factor in the high pressure compaction of residential
solid wastes.
Considering, in particular, the need for at least
one stable dimension of the bale, it is critical to
determine not only the over-all springback volume
and time, but, specifically, the dimensions of any
directional orientation of the springback if such
pattern exists. The directional patterns of the
springback determine primarily, of course, the
dimensions of the compression chamber and the
loading configurations of the bales for solid-waste
rail-haul.
As a result of these deliberations it was decided
to ascertain very carefully any directional orientation
of the springback and to prepare the equipment
specifications in terms of the bale dimensions
indicated in Table 4 and the previous discussions.
d) Stability of the Bales
The requirements of a specific bale form and size
necessitate that the bales be stable. Without stability
there would be no control of form or size. Thus, the
bale must hold together for a given period of time
and be suitable for transport and material handling
during that period of time.
In terms of time, solid-waste rail-haul is
contemplated currently to include once-a-week
pickup schedules for certain system configurations.
Thus, a bale could be 7 days old before the beginning
of the shipment and, assuming a 2-day rail transit, it
could be 9 days old before placement in a landfill.
In terms of transport, the current rail-haul system
developments include shipment distances of up to
150 miles. Consequently, bales 9 days old should be
suitable for rail transport of that distance and, of
course, be capable of withstanding the system
associated material handling operations as well.
In analyzing the stability requirements it must,
however, be recognized that bale stability can be
produced by various means. For example, it might be
achieved by the application of pressure alone, by the
addition of adhesives before or during the baling
operation, and by encapsulation and/or strapping
after the bale exits from the press.
After evaluating these alternatives it was decided
TABLE 4
Approximate Patterns for Various Bale Sizes, as Suggested
by Rail-Freight Car Loading Constraints
Bale Dimension ft
Width
(feet)
9.00
k.50
3.00
2.25
1.50
1.12
1.00
1 ternat ives
Maximum
8.0
4.0
2.0
1.0
in Terms of a Sta
Height
(feet)
or Variable
ii
ii
ii
ii
1 1
ii
ndard Rai 1 Car
Length
(feet)
Variable
ii
n
ii
n
1 1
n
18
-------
to emphasize first, of course, the production of bale
stability by the application of pressure alone, and to
investigate other alternatives only in case of need.
Thus, within reason, the investigation of pressures
higher than those needed for mere volume reduction
becomes an important project objective.
Finally, since the application of various stability
aids presupposes different conditions of the virgin
bale, it was decided to ascertain the bale stability by a
variety of methods ranging from visual observation to
vibration and impact tests. Specifically, it was
decided to develop a simple and fast stability
evaluation method suitable for production-line
operations by relatively untrained people.
4. Process Performance Requirements in Terms of
Public Health and Environmental Control
Any development of new technology dealing
with the disposal of solid wastes must, of necessity,
consider the public health and environmental control
hazards that might arise. Specifically, it must be
ascertained whether or not the process by itself
introduces a type and degree of pollution which is
more severe than that caused by currently acceptable
solid waste disposal operations. In terms of rail-haul,
pollution might be introduced or reduced by the
results of processing at the transfer station, during
transit, and at the disposal site.
It must be recognized, of course, that almost all
solid waste mixtures contain pollutants regardless of
whether the materials are processed or not. Thus,
pollution control research becomes critical in the
development of new solid waste disposal technology
only if (a) the process by itself causes a type of level
of pollution which violates existing control standards
and (b) cannot be dealt with in a suitable manner by
already existing pollution control methods. If the
process itself does not cause such a level or type of
pollution, then the problem obviously does not exist.
To ensure the best allocation of the available
effort, funds, and time it was decided, therefore, to
undertake pollution control research only in case of
apparent need. In the absence of such need, it was
decided to rank pollution control through the
compaction process among the benefits of the process
or the highly desirable process refinements.
5 Process Performance Requirements
In Terms of Cost
Waste, by definition, has no economic value.
However, in economically developed, urbanized
societies, waste not only lacks any economic value, it
even has a negative economic value. In the United
States, for example, solid waste disposal burdens the
economy annually with $4.5 billion of unreturnable,
though necessary expenditures in addition to the
indirect costs resulting from the destruction or
impairment of the environment.
In view of this situation, it is critical for the
development of any new solid waste disposal
technology to seek minimum cost approaches
consistent with environmental control right from the
beginning of the initial endeavors. Consequently, and
considering particularly the constraints of this
project, it was necessary to de-emphasize process
improvements which might be desirable but which are
not absolutely required for the establishment of a
workable, acceptable, initial solid-waste-high-pressure
compaction.
Correspondingly, it was decided to allocate as
much effort as possible to the investigation of areas
promising process economies exceeding those readily
available at the present time. Specifically, it was
decided to explore the feasibility of cost reduction in
the equipment implementation, e.g., the press,
through an initial conceptual investigation of
alternative design approaches.
HI. THE IMPLICATIONS OF
THE PROCESS PERFORMANCE REQUIREMENTS
FOR THE SELECTION OF THE RESEARCH PRESS
Limitations in time and funds eliminated the
possibility of building a compaction device
specifically designed for the purposes of this research
project. As a result, it was necessary to make a
judicious basic selection among the many types and
sizes of secondhand equipment readily available.
Simultaneously, it was necessary to consider carefully
the possibilities and cost of making the necessary
adaptations on the equipment that might be
obtained.
1. The Selection of the Basic Type
Of Compaction Equipment
Industry uses a wide variety of machines to force
or form materials into desired shapes by the
application of pressure. The pressures may be
generated by hydraulic, pneumatic, or mechanical
means of force development and force transmission.
Furthermore, the pressures may be applied by
pressing, hammering, or rolling.
Based upon the scope of the project and on both
the type of materials to be compressed and the form
of output desired, it was decided to use pressures
applied by pressing. Rolling was excluded because it
does not per se produce a bale or "package".
Hammering was excluded because the maximum
force is applied by short impact while the materials to
be compacted, e.g., paper, may require a gradual
application of pressure for maximum compaction
19
-------
effects.
In terms of pressure force development and force
transmission, it was decided to use a hydraulic press.
Pneumatic presses are generally not built for pressure
applications of about 2,500 psi, the pressure
suggested by the exploratory research of the APWA
rail-haul study team—and thus required for this
compaction research project. Mechanical presses
cover much of the same range in the maximum
application of pressure as hydraulic presses. Also,
they are, as a rule, faster than hydraulic presses, easier
to maintain, and more efficient to operate because of
the energy-storing flywheel.
However, within the constraints of a given single
device, hydraulic equipment is more flexible and also
more easily adjustable to meet varying requirements.
Press requirements which were considered for this
research project include: (a) the application of
selected pressures below the maximum force, (b) the
application of pressure increments at regulated
intervals, (c) the holding time of a given pressure
application, and (d) the application of pressure to
specimens varying significantly in their ultimate size
after compaction.
Finally, the selection of the press was made in
consideration of the properties of the materials to be
compacted. The characteristics of solid waste
compositions require that the force be applied to the
materials in an enclosed chamber. Considering the
flow characteristics of semi-solids, e.g., mud,
compression without an enclosed chamber would
allow the materials to escape and an effective
application of pressure could not take place.
Thus, for the purposes of this research project, it
was decided to select a hydraulically operated press
capable of applying upwards of 2,500 psi to
solid-waste materials in an enclosed chamber. This
selection, of course, does not imply that pneumatic
or mechanical force development and transmission
methods cannot be used alone or in combination with
hydraulic methods in the high pressure compaction of
solid wastes.
2. The Selection of the Compaction
Equipment by Speed of Pressure Application
The available literature indicates that cycle times
of 30 seconds are not uncommon for modern
hydraulic presses operating in the pressure range
required for this project. This implies that,
theoretically, two bales of solid waste could be
produced per minute.
Consequently, to fully explore the actual
potential of compaction developments, the research
press was required to be capable of applying the
relevant compaction pressures within a time span of
less than 30 seconds.
3. The Selection of Compaction
Equipment by Size
The process performance requirements outlined
above were used to identify parameters for the
selection of the press in terms of size. In this context
size refers to the dimensions of the compaction
chamber and the volume reduction ratios
incorporated in the over-all design of the press.
a) Dimensions of the Compaction Chamber
The dimensions of a suitable compaction
chamber were derived by consideration of the
interrelationship between over-all throughput ratings,
' the potential sizes of various bales, a set of density
postulates, and the number of bales that ultimately
might be made per minute. Thus, a set of progressive
computations was required to identify a suitable
compaction chamber size.
The over-all process throughput ratings or
requirements, illustrated in Figure 1, can be
converted to the corresponding weights per bales as
shown in Table 5.
To obtain perspective, these weights calculated
per bale must now be correlated to the potential sizes
of the ultimate bale. Based upon the bale
configuration in the form of a cube and the bale
loading dimensions developed previously, the
potential volume alternatives are given for the
ultimate bale after springback in Tables 6 and 7.
The correlation between bale weight, Table 5,
and bale volume, Table 6, is presented in terms of
pounds per cubic foot in Table 7 on the following
page. The data in Table 7 are then evaluated in terms
of the densities estimated on the basis of the
exploratory research conducted by the APWA
rail-haul study team and reported in the rail-haul
interim report. The density values, falling within the
range of 60 to 130 pounds per cubic foot, are
indicated in Table 7 by underlining.
The data developed in Table 7 can already be
used to indicate desirable press-size benchmarks.
Thus, in terms of guidelines underlying this project,
the 4.5- and 1.0-foot bales are completely outside the
scope of potential development goals. The densities
correlating to these two bale sizes are found to be
either too high or too low. Considering the four
remaining potential bale sizes, the data dictate that,
in case of need, priority be given to the 2.5- and
1.50-foot bale.
Finally, it must be stressed that the data in Table
7 refer to bales after springback. Consequently, a
press still would be suitable if the dimensions of its
compaction chamber were smaller. Assuming
springback variations of 33, 50 and 100 percent, the
corresponding volumes of the compaction chamber
are shown in Table 8.
20
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TABLE 5
The Weight of Solid Waste Bales in Terms of 360 Minutes
Effective Press Operations, Varying Overall Throughput
Requirements, and Variations in the Number of Bales
Produced Per Minute*
Overal 1
Transfer Station
Throughput Requirements
(Tons /8-hr Shift)
500
250
100
50
Correspond ing
Press Throughput
Per 360 Minutes
Actual Working Time
(Tons per Minute)
1 .1*0
0.70
0.28
0.14
Weight per Bale
Per One
Bale/
Minute
(Ibs)
2800
1400
560
280
Per Two
Bales/
Minute
(Ibs)
1400
700
280
140
*Some data are slightly rounded.
TABLE 6
Bale Volumes Corresponding to Variations
in Selected Bale Dimensions Derived
from Rail Car Loading Dimensions
Side of Cube*
(feet)
4.50
3.00
2.25
1.50
1.12
1.00
Volume of Bale
(cubic feet)
91.12
27.00
11.39
3-37
1 .40
1.00
* See Table 4
21
-------
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22
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As a result of these data and deductions, it was
concluded that a press would still be suitable for this
research project if the volume of its compaction
chambers were such as to allow for reasonable
extrapolations of the test results to compaction
chamber dimensions varying from 1.68 to 8.54 cubic
feet. Ideally, it would, of course, be desirable if the
dimensions of the research press compaction chamber
would support extrapolations to cover the total range
of the chamber sizes indicated in Table 8.
In evaluating the above compaction chamber size
data, it must be recognized that they are based on the
production of one or two bales per minute. This high
speed of production allows the compaction chamber
to be rather small but still suitable for the throughput
requirements as dictated by the transfer station
capacity ratings. Other operational press
configurations are, of course, possible. A 1.4 ton
throughput per 1 minute is, for example, the
equivalent of a 4.2 ton throughput per 3 minutes, if
the bale size is increased from 2,800 to 8,400 pounds
per bale. However, even at a density of 100 pounds in
the compaction chamber, the chamber would have to
have a volume of 84 cubic feet or approximately 4 x
4x5 feet, which exceeds by far the dimensions of
secondhand presses readily available. Thus the above
calculations address themselves to the suitability of
the secondhand presses available rather than to the
dimensions of presses that might be built for the high
pressure compaction of solid wastes.
b) Volume Reduction Potential
As is well known, solid wastes can be rather
voluminous. Densities of loose household refuse are
reported to vary from 100 to 270 pounds per cubic
yard or 3.7 to 10 pounds per cubic foot.
Thus, assuming an ultimate density after
springback of about 50 pounds per cubic foot and
assuming a minimum springback of about 33 percent,
the density in the compaction chamber would
amount to 75 pounds per cubic foot or about 2,000
pounds per cubic yard. In view of these data, it was
decided to obtain a press in which the ratio between
the volume of the charging box and the effective
volume of the compaction chamber would be 15:1,
or larger.
IV SUMMARY OF THE OPERATIONAL
GUIDELINES UNDERLYING
THE EXECUTION OF THIS PROJECT
On the basis of the information presented in
Section Three of this chapter, it was possible to
develop a simple operational code, or basic
operational procedure, for this project. To put the
necessity for this code into perspective, it must be
recognized that the project deals with a subject which
is not only very complex in itself, but also very
susceptible to the inclusion of many additional
research objectives and aspects.
The operational guidelines emerging from the
findings, analyses, and evaluations indicated in
Chapter II can be summarized as follows:
1. Confine the compression tests to residential
solid waste mixtures and their components.
2. Base the process developments on material
throughput or capacity ratings of 0.14 to 1.4
tons per minute.
TABLE 8
Compaction Chamber Bale Volumes Based on Various
Amounts of Springback*
Vol ume of the
Bale After
Spr i ngback
(Table 7)
(cubic feet)
27.00
11.39
3.37
1 .kO
Compaction Chamber Volume
Based upon a Springback of
332
(cubic feet)
20.25
8.5*»
2.52
1.05
50%
(cubic feet)
18.00
7-59
2.25
0.93
100%
(cubic feet)
13-50
5.68
1.68
0.70
*Data slightly rounded.
23
-------
3. Try to achieve average material shipment
densities of at least 50 pounds per cubic foot.
4. Avoid the investigation of very low or very high
pressure applications, if they do not relate to the
volume reduction or stability requirements of
this project.
5. Give priority to the development of square or
rectangular bales. Consider other configurations
only in case of need.
6. Limit the developments to a maximum of four
ultimate bale sizes—one of their sides being 1.12,
1.50, 2.25 or 3.00 feet. If necessary concentrate
the research efforts on the 1.50-and 2.25-foot
bale.
7. Determine carefully the amount and, in
particular, _any directional orientation of
springback occurring in the bales after exit from
the press.
8. Develop bales which are stable for 9 days and
suitable for rail transport of up to 150 miles
within this time period.
9. Emphasize the application of pressure for
achieving bale stability. Investigate other stability
aids only in case of need.
10. Check for pollution caused by the compaction
process itself. Engage in pollution control
research if compaction by itself causes any form
of pollution which cannot be handled in an
acceptable manner by existing control methods.
11. Orient all investigations toward the establishment
of a compaction process of minimum cost.
Investigate specifically avenues of possible
equipment development which promise cost
reductions and thereby will foster a more
widespread application of the high pressure
compaction process.
12. Obtain a hydraulic press which
a) is capable of applying relevant pressures
upwards of 2,500 pounds per square
inch within a time span of less than 30
seconds to solid waste materials in an
enclosed chamber,
b) has dimensions of its compaction
chamber which can support an
extrapolation of the test results to
compaction chamber dimensions ranging
from a minimum of 1.68 to 8.54 cubic
feet to- a maximum of 0.70 to 20.25
cubic feet, and
c) provides an in-press volume reduction
potential of at least 15:1.
These guidelines were applied constantly
throughout the project to both the problems
encountered and the findings as they developed. Thus
these guidelines determined ultimately the scope as
well as the depth of this project's total results.
Correspondingly, these guidelines must be kept in
mind in evaluating the project findings. Although
many of this project's efforts deal with physical
science phenomena, they are conditioned by the
experimental setup and constraints. Thus some of the
results are, for example, peculiar to the press used or
the process operations pre-supposed, while other
results are independent of these constraints. The
limitations of the project did not allow attempts to
dimension the effects of such constraints by
investigations specifically oriented toward this
purpose. It is therefore recommended this research
aspect be included in any follow-up project that
might be contemplated.
24
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CHAPTER 111
THE HIGH PRESSURE COMPACTION
OF SOLID WASTE MATERIALS
The main objective of this part of the study was
to gather technical data necessary for the
development of a suitable process which could be
utilized both to decrease the volume of wastes and to
produce cohesive refuse bales stable for rail:haul
handling and transport.
In order to achieve the above objective,
experiments were carried out to study the effects of
waste compositions and compaction conditions on
bale formation and the resulting bale properties.
The experimental setup and experimental
techniques used or developed are described in Section
One. Additional experimental information pertaining
to sets of specific experiments is presented at
appropriate places in the other chapters. Section Two
contains a description of the wastes used in the study
and Section Three presents the results of the
compaction experiments as well as the interpretation
of these results.
SECTION ONE-EXPERIMENTAL SETUP,
PROCEDURE, AND MEASUREMENT
DEVELOPMENT
This section describes the hydraulic press used
for the compaction of wastes, the operation of the
press, the electronic measuring system attached to the
press, and the measuring procedure. It also presents
the experimental setup and findings of three
measuring methods investigated during this program
and designed to study the development of forces
during bale formation.
I. EXPERIMENTAL SETUP AND PROCEDURE
The experimental setup used for the compaction
of wastes consisted of a three-stroke hydraulic press
and attached electronic measuring equipment.
1. Compaction Press
The press, donated to the project by General
Motors Corporation, was a 17-year-old normal metal
scrap baler which was reconditioned and modified. A
sketch indicating the three-stroke arrangement of the
press is eiven in Figure 3.
The original water-oil emulsion system was
converted to an oil hydraulic system. In addition, the
total force of the high pressure ram (third ram) was
increased from 430 tons to 610 tons by the addition
of two, 8-inch diameter booster cylinders. Another
modification introduced into the press was the
addition of a series of ram locks powered by a
separate 2,000 pounds per square inch hydraulic
system.
The ram lock system consisted of six, 6-inch
diameter cylinders, one cylinder holding the rolling
cover at the top of the press box in place, three
cylinders holding the low pressure gathering ram (ram
1) in place, and two cylinders holding the
intermediate ram (ram 2) in place. The locks were
provided to prevent the movement of the first and
second low pressure rams and the cover during the
final high pressure compaction. This was found
necessary because previous observations indicated
that high expansion forces can be created during the
compaction of refuse.
The opening and closing of the cover, and the
return movement of the first and second ram was
accomplished by the use of compressed air from a
Worthington air compressor and a low-pressure air
accumulator. Hydraulic power was supplied to the
system by two double-end pumps. These pumps were
capable of delivering 83 gpm of oil at 1,250 psi, and
55 gpm at 3,500 psi, respectively. The pressure of the
second pump was limited to 2,500 psi by a Vickers
relief valve. Each pump was driven by a 75 hp, 1,200
rpm electric motor connected to a multiple "V" belt
drive. The return of the third ram was accomplished
by gravity.
The gathering ram (Ram 1, Fig. 3) was mounted
horizontally in the press. The dimensions of this ram
were 60 x 42 inches in platen face area and 11 inches
in ram diameter. It was calculated that the ram exerts
a total force of 119 tons, or 94 psi, for a line pressure
of 2,500 psi.
The intermediate ram (Ram 2, hig. 3) was also
located horizontally but at a 90 degree angle to the
gathering ram. The area of the platen face of this ram
was 42 x 16 inches and the diameter was 14 inches.
The total force exerted by the intermediate ram was
calculated to be 192.5 tons, or 573 psi for a line
pressure of 2,500 psi.
The high pressure ram (Ram 3, Fig. 3) was
originally powered by an 18-inch diame-ter
single-acting cylinder which developed 430 tons. The
addition of two 8-inch diameter single-acting booster
cylinders increased the available force to 610 tons, or
3,769 psi, across the 16'x 20 inch platen face.
However, a cutoff valve installed in the system
reduced the utilized pressure to about 3,500 psi. The
calculated unit pressure of this ram was equal to the
line pressure times a factor of 1.11.
An Oilgear 3/8-inch relief valve, having a pressure
25
-------
Gathering Ram
(Ram 1)
Charging Box
Intermediate Ram
(Ram 2)
A
^High Pressure Ram
(Ram 3)
FIGURE 3
Compaction Press
26
-------
range of 500 to 5,000 psi, was installed during the
program to provide fine control of the system's oil
pressure to the rams.
2. Press Operation
The press was operated manually. The press
operator initiated all operations with the exception of
the safety locks which were automatically actuated
by limit switches.
The procedure of operating the press durino
compaction was as follows:
a) All pumps were started and the air circuit
was brought up to pressure.
b) A premeasured charge of refuse was loaded
into the.open charging box.
c) The charging box was closed by advancing
the cover on top of it.
d) The cover was locked into position.
e) The gathering ram was then advanced and it
too was locked into position.
f) The same operation was again repeated with
the intermediate ram, and after its locks were
in position, the high pressure ram was ready
for operation.
g) The high pressure ram was then advanced
until it reached a predetermined pressure,
and the compaction was completed.
h) To. remove the bale from the press, all three
rams were first rrjoved slightly out of
position to remove the pressure from the
bale.
i) After removal of the cover plate from the
top of the box, the third ram was again
activated to eject the finished bale out of the
charging box.
3. Measurements of Press Parameters
An electronic measuring system was installed to
allow the measurement of several press functions:
a) Ram displacement of the high pressure ram;
b) Hydraulic pressure of the high pressure ram;
and
c) Ram displacement of the intermediate ram.
These functions were sensed with transducer
elements that converted the input variables to electric
signals. These signals were then amplified and used to
drive recording styli to produce time-history records
of the event. At a later stage of this work a second
output device was added to produce a direct plot of
the applied pressure versus the displacement of the
third ram.
Functionally, all three signals were processed as
shown in Figure 4.
The individual elements of the measuring system
are described in the following paragraphs.
Block A: Pressure Transducer
The hydraulic pressure to the high-pressure ram
was measured by a Transducer's Incorporated Gage,
Model GP 56F-7500. This is an electrical gage
assembly in which the applied pressure produces a
force which loads a column. Electrical gages sense
strains in the column as it deforms during the
application of pressure. The strain gages were wired in
a Wheatstone bridge configuration so that an output
"P" Input
Pressure
(Ram 3)
Pressure
Transducer
-
Amp.
"A "Input
1
Displacement
(Ram 3)
Di splacement
Transducer
D
P Plotter
P £ A
vs .
A Time
' — >
E
P Plotter
P
vs .
A A
FIGURE 4
Electronic Measuring System Diagram
27
-------
voltage develops from the bridge as pressure is
applied.
Block B: Deflection Transducer
The two deflection or position transducers used
in the setup were Model WR8 50A manufactured by
the Lockheed Electronics Company. Basically, these
gages are electrical potentiometers whose slider
position is controlled by the extension of a
measurement cable. Thus, if a voltage is impressed
across the ends of the potentiometer resistance, the
voltage measured between the slider and either end of
the resistance will be an electrical analog of the
position of the slider and/or the extension of the
cable.
Block C: Signal Amplifying Equipment
Equipment used for the supply of power to the
gages and to amplify the signals from the recorder
was manufactured by Electronics Limited, Series
2800. The signal conditioning equipment contained
all the necessary controls to power the gages, adjust
their balance points, control the sensitivity of the
measurements, and calibrate the pressure channel.
Block D: Two-Channel Plotter
The two-channel, time-base plotter used was the
Model TR 722 manufactured by Technirite
Electronics. It provided a chart record of two input
signals versus time,at different paper speeds and signal
sensitivities.
Block E: Two-Channel Plotter
This plotter was a Mosely 2D series instrument
which recorded the pressure versus displacement on a
graph. It utilized the same signal input as the TR 722
but contained its own controls of sensitivity and
positioning.
4. Calibration of the Deflection and
Pressure Measuring System
Each run of the press provided a check of the
deflection calibration system of the high pressure
ram, since the ram always started its travel from a
zero position and, as the bale was ejected, reached its
full extension. This known travel distance was used to
set the sensitivity of the deflection channel.
Calibration of the pressure measuring channel
was by signal substitution: the electrical signal whos.e
pressure equivalent had been established could be
injected into the channel by operation of a
push-button control. The equivalence to pressure was
established at the test site by subjecting the pressure
transducer to an accurately known pressure from a
dead weight pressure gage calibrator.
II. DEVELOPMENT OF METHODS FOR
THE MEASUREMENT OF FORCES AT THE
BALE-PRESS INTERFACE AND
WITHIN THE BALE
In addition to measurements of press parameters,
as described in the previous section, an attempt was
made during the study to measure the forces active in
bale formation. This was done since a knowledge of
the various forces developed in the press frame, at the
bale interface, and within the bale are of importance
both with respect to press design and for the
understanding of the compaction process.
Furthermore, information of this type and
applicable to the compaction of wastes is found to be
nonexistent. To complicate matters, it was also found
that standard measuring techniques and methods
which can be used for the determination of these
forces are not easily adaptable to refuse compaction
and that new methods have to be developed or
adapted.
Ideally, measurements should be taken of the
magnitude of the forces, the various displacements
and density distributions within the bale, and of the
normal and shear forces at the bale and chamber
interfaces.
Due to the limitation of time and manpower, the
exploration and development of suitable techniques
had to be limited. Nevertheless, an appreciable
amount of work was done and several approaches
were evaluated. One of these approaches showed
great promise; it utilized penetration gages for
measurements at the interfaces between the chamber
walls and the refuse. The resultant force
measurements obtained by this method are presented
in Section Three.
Initially, it was necessary to establish the general
mechanics of refuse bale formation to ascertain
whether a particular approach merited further
investigation. Since uncompressed refuse occupies an
appreciably larger volume than compacted refuse, the
mechanics of the process involves movement of the
refuse during compaction. In a three-stroke press, as
used in this study, the movement of the refuse into
the final space is accomplished by the successive
movement of each ram located at different angles.
This results not only in a change of the initial
position of the refuse, but also in successive changes
in the position of the individual items in the refuse
subjected to forces applied from different directions.
28
-------
The above facts indicate the high probability of
failure of any method which utilizes electrical leads
and connections between the gaging elements placed
inside the refuse and the outside of the compaction
chamber. Thus it was decided to explore only those
methods for measurements of forces within the bale
which would be self-contained. This dictated the use
of mechanical gages of the "peak reading" or "final
reading" type.
The measurement of forces at the bale-chamber
interface was attempted in two ways: one utilized
electrically gaged liner plates in the compaction
chamber, and the second used a mechanical gage
assembly specifically constructed to cover the area of
the high pressure ram face.
A description of the various methods tested and
their evaluation is given in the next sections.
1. Measurements within the Bale
Pressures developed within the bale during
compaction were measured with locally
manufactured small penetrometer gages. Each gage
occupied a volume of about 1/4 cubic inch. It was
essentially a sandwich-type construction of two 1/2
inch square, 1/8 inch thick steel plates, with a
hardened steel ball placed between them. A sketch of
the gage assembly is shown in Figure 5. To hold the
two plates parallel and avoid movement of the ball
from its proper position, the gage assembly was held
together by a soft wax and coating of tape.
i n I
F°rce
t t t T
Force
FIGURE 5
Penetrometer Gage
The application of forces normal to the two
planes of the gage introduces high-contact stresses
between the ball and plate. These stresses produce
local deformations in the plates, resulting in circular
depressions. The diameters of the depressions are
related to the applied force. Although the
relationship is not linear, reasonable linearity can be
obtained in a given pressure range by proper selection
of ball diameter and plate hardness.
One of the features inherent in this gage is its
strength to normal forces and its weakness with
respect to applied shearing forces. In the presence of
significant shear forces the gage is likely to separate
into its individual elements. In the case in which the
shear forces would be developed after initial normal
forces were applied, the penetration marks were
expected to be elliptical rather than circular.
Several tests were carried out to ascertain the
applicability of these gages for internal" force
measurements in the bale. The gages were either
randomly distributed in the loose refuse or were
interconnected with Scotch tape and attached to
specific refuse items. The refuse was compacted and
the compacted bales were then dissected in order to
retrieve the inserted gages, and to determine the
location and orientation of the gage assembly within
the bale.
Difficulties were experienced with respect to the
retrieval of the gages inside the baled refuse, since
their movement during compaction could not be
p:udicted. Similarly, it was difficult to avoid
displacement of the gages from their positions during
retrieval. This impaired the determination of the
exact orientation of the gages, with respect to the
applied force in the bale, a requirement necessary for
the evaluation of the measured force.
Of the 25 gages inserted into the refuse, two had
sheared and separated into their elements. Five gages
showed noticeable elongations of the indents.
However, the track width did not vary significantly,
indicating shearing and constant normal forces. The
other gages showed clean indentations; however, the
indentations were, in most cases, very slight.
Measurements taken from the gages indicated
that the peak force was probably applied to the bale
only during the final few inches of compaction. Thus,
it seems valid to assume that in the majority of cases
the measured peak force would represent the force
applied to the gage at, or very near, its final
orientation.
Although the results showed that the approach
had promise, it was clear that the necessary
refinements of the method would require more time
than was available during the present study. It is
recommended, however, that the investigation of this
method be continued in a future study.
2. Measurement of Forces at
the Press Chamber Walls
In order to measure the forces developed at the
chamber walls of the press and their development
with time, the liner plates of the chamber were
equiped with strain gages. It was hoped to measure
both normal and shear forces during bale formation
on at least three faces of the press.
29
-------
Limitations of strength within the press structure
and the arrangement of the ram system of the press
did not allow the insertion of a system occupying a
larger volume than the available space within the liner
plates. These plates were removable sections used to
protect the heavy steel outer box which provided
strength for bale formation. The thickness of the liner
plates was only three-quarters of an inch.
Due to the limitations in thickness of the plates
and the need to place all gaging and wiring on the
backside for protection, a simple clamped diaphragm
sensing element was selected as a measuring device.
The sketch below (Fig. 6) shows tha arrangement.
To form the diaphragm section and gage cavity,
metal had to be removed from the liner plate. This,
naturally, introduced a discontinuity in the liner plate
wall stiffness which could affect the measurements.
In addition, the bulk modulus of the waste materials
was not known and as a result its effect on the
measuring system could not be predicted. It was
decided, therefore, to test one gaged liner plate
outside the press.
The gaging of the liner plate was based on the
following considerations:
a) Application of a distributed normal force
produces tensile strains in the center lower surface of
the reduced section of the liner plate. These forces
are sensed by an attached electrical strain gage. If the
forces are uniform and normal then the isostrain lines
form concentric circles about the center.
b) Application of a shear force will distort these
circles. Thus, it was reasoned that by a judicious
location of a number of strain gages in the plate, a
good measure of the normal force and a fair measure
of the shearing force could be obtained.
c) It was calculated that for a safety factor of 2,
at rated nominal working force, and a
diameter-to-thickness ratio of 7.52, the diameter of
the machined cavity in the 3/4-inch plate must be
approximately seven and one-half times the thickness
of the diaphragm. For a diaphragm thickness of 0.222
Force
inches the minimum space requirement of gage
location, wiring, etc., was found to be about 1-5/8
inches. Gaging elements conforming to these
dimensions were installed in a plate.
The gaged plate was tested by application of
known loads applied on a 4-inch diameter, circular
loading platen in a standard testing machine. A
variety of waste materials was placed between the
loading platen and the gaged plate. These included
paper sheets of various thicknesses placed either
parallel or perpendicular to the gaged plate, rubbers
of different thicknesses, lead, lead discs, and shredded
paper. The results of the tests are plotted in Figure 7.
It can be seen that the plots of gage response
versus transmitted load which were obtained for
different materials were, in the majority of cases,
appreciably different from the predicted response
curve.
In addition, with the exception of the
experiments carried out with paper sheets placed
vertically to the gaged plate (8, 9, 10), the resultant
measured load was found to be lower than the
expected value.
Load values obtained from lead, rubber, and
shredded paper were close to the predicted values. In
each case in which paper sheets were placed
horizontally to the gage plate, much lower values
were recorded. Vertically placed paper simulated, in
most cases, higher load values than actually applied
but lower values were also obtained.
The large spread of the load versus response
curves obtained for paper alone indicate the strong
effect of its configuration with respect to the gage
sensing element. Point loading most likely (vertically
placed paper) led to steeper curves simulating in the
upper pressure region a higher pressure than was
actually applied. When, paper sheets were placed
horizontally the material apparently acted as a bridge
across the more deformable sensing area. As a result,
the diaphragm experienced a lesser load than applied,
and the stiffer area—the solid plate adjacent to
I i 1 i 1
3/V'
Strain Gaqes
lN
Liner Plate
> ^ \ '
Frame
FIGURE 6
Strain Gaged Liner Plate
30
-------
CT» CO
CO
Q.
O
•o
O
CO
o
-o
o
CM
K o
O o
O
.c
'cd
in
UH
o
c
o
-§
O
o
o
O
O
LA
O
O
-3-
O
O
O
o
CM
O
O
ssuodsay
461-084 O - 72 - 4
31
-------
it—carried the main load. The curve obtained for
shredded paper was found to be closest to that
predicted.
The results indicated clearly that the gaged liner
plates as used in the tests were not suitable for
measurements of the wall forces produced during
compaction. The shortness of the project precluded
further investigation of different approaches utilizing
the same principle.
3. Chamber Wall Measurements Using
Penetration Gages
After the electrically gaged liner plates were,
within the' scope of this project, found to be
unsuitable for chamber-wall force measurements, a
different approach was tried. A gage assembly was
constructed utilizing the experience gained with the
ball penetrometer gages for internal force
measurements.
Two plates, of an area equivalent to the high
pressure ram face (16 x 20 inches), were constructed.
Balls were placed at regular intervals between the
plates. Only one of the two plates was designed to be
penetrated; the other was used to distribute the load.
The penetration plate was constructed from 1/8-inch
aluminum sheeting. The load distributing plate was
6000 [-
made from a 3/16-inch steel sheet. The entire
assembly, including the balls, was 9/16-inch thick.
The penetration gage assembly contained 252 balls,
and therefore allowed peak measurements of the
normal force at 252 points.
In order to maintain proper ball spacings, the
plates were fastened at two edges to a narrow filler
plate. This filler plate extended only 1/4-inch
between the edge of the plates. The filler was also
used to minimize the entry of waste materials
between the plates during the compaction process.
Calibration of the indentations of the ball
elements was performed in a laboratory testing
machine. A known load was applied and the
indentations were read by microscope to a precision
of about ± 200 pounds for loads above 2,000 pounds.
The precision of the readings was higher for lesser
loads. The over-all accuracy of the measurements over
the whole range of pressure was better than 10
percent. The calibration curve shown in Figure 8, was
found to be somewhat non-linear, but quite
reproducible.
To test the applicability of this gage to refuse
compaction, several experiments were carried out.
Only one plate assembly, next to the high-pressure
ram face, was used in most cases. However, in a few
cases two plate assemblies were inserted into the
in
.a
5000
4000
.?! 3000
Q.
Q.
2000 L
1000 L
10
20
30
50 60 70 80
Penetration Diameter
FIGURE 8
Penetration Gage Calibration Curve
32
-------
compaction chamber, one on the top of the
high pressure ram, and the other directly opposite the
same ram adjacent to the cover plate of the press.
After the compaction experiments were completed
the plates were removed from the press and analyzed.
Analysis of the plates and their indentations
showed that the load values were slightly higher than
they should have been. This effect can be accounted
for by the fact that the ball area, which is the sensing
area, was stiffer than the area between the balls. The
close spacing of the balls, and the properties of the
steel plate acting as a non-rigid diaphragm, minimized
this effect. The calibration curves obtained for
different waste materials were all similar.
Although the investigation and application of the
above method could not be fully explored, the results
showed clearly that valuable information can be
obtained from it. The results of the penetration gage
measurements obtained for refuse and their
interpretation are discussed in the section on the
compaction of wastes, Section Three.
SECTION TWO-DESCRIPTION OF THE SOLID
WASTES USED IN THE STUDY
This section describes and discusses the
properties of the uncompacted wastes which were
subjected to compaction. It includes a description of
different types of (I) residential wastes as delivered
by truck and of (II) synthetic refuse samples specially
prepared for this study. The composition, moisture
content, and densities of the uncompacted refuse are
discussed in some detail.
I. RESIDENTIAL REFUSE
For the purpose of this report the household
refuse used during the compaction program has been
subdivided into six different categories'
a) Residential Refuse-loose
b) Residential Refuse-shredded
c) Residential Refuse—in paper sacks
d) Residential Refuse-in plastic sacks
e) Oversized Wastes (refrigerators, furniture,
stoves, washing machines, appliances), and
0 Mixtures of oversized wastes and household
refuse
1 he above subdivision has been made in view of
both the existing collection practices and the
differences encountered in the compaction behavior
of the wastes delivered in different forms.
I. Composition and Moisture Content of Loose,
Sacked, and Shredded Residential Wastes
The composition and moisture content of the
individual samples of loose, shredded, paper-sacked
and plastic-sacked household refuse used for testing
varied appreciably. However, the effects of
composition and moisture content on the compaction
of wastes were found to be pronounced only for
extreme variations introduced either by drastic
seasonal changes in the refuse composition or by
weather conditions which increased the water content
of the wastes.
In the over-all, the waste mixtures from
households were of similar composition during the
same season irrespective of whether the mixtures
were confined in paper or plastic sacks, shredded, or
delivered in the loose state. The moisture content of
the various mixtures, however, varied appreciably
with weather conditions. It was highest for loose
refuse during rainy days, while rain had little or no
effect on the moisture content of sacked refuse.
a) Composition of Winter and Spring Refuse
Two types of seasonal retuse were subjected to
compaction during the testing period, which lasted
from January 28, 1969, through April 1969. The
two types are classified as winter refuse and spring
refuse.
The composition of these two types of refuse
varied markedly. The winter refuse was largely
TABLE 9
Composition of Dry Winter Refuse
Components in Percent of Total Weight
(averages)
PAPERS
(Sol ids
and
absorbed
1 iqu ids)
70
GLASS &
CERAMICS
6
METALLIC
WASTES
6
FOOD
(Sol ids
and
bound
water)
5
PLASTICS
3
TEXTILES
(Sol ids
and
absorbed
water)
3
RUBBER, DIRT
CHEMICALS, ETC.
7
33
-------
composed of paper products. The paper content of
the individual loads was estimated to range from
about 50 to 80 percent by weight of the total refuse.
An estimate of over-all composition of dry winter
refuse is given in Table 9.
In order to obtain some estimate of the over-all
composition of the spring refuse, samples were taken
over a period of days and separated manually into
different components. The composition, as identified
for 18 samples, each of an average weight of 176
pounds, is given in Table 10.
Moisture determinations of samples of loose
household refuse during dry, snowy, and rainy
weather ar,e given in Table 11. The values for samples
takerrfrom the same load of refuse are days or from
different loads.
The moisture content of loose and sacked refuse
samples taken during dry weather conditions varied
from 10 to 35 percent by weight of the total refuse.
Variations of up to 20 percent were found in samples
taken from the same load. The highest moisture
content of the dry weather refuse was associated with
TABLE 10
Composition of Springcleaning Refuse
Components in Percent of Total Weight
(averages)
PAPERS
(Solids
and
absorbed
1 iquids)
%
47.0
YARD
RAKINGS,
Dirt (£
moi sturc)
%
17.1
GLASS &
CERAMICS
%
12.2
FOOD
(Solids
and
bound
water)
*
9.6
TIN CANS
%
9-3
RAGS,
SHOES &
Moisture
%
2.5
PLASTICS
%
2.4
The refuse received from the City of Chicago
during the spring period contained a large proportion
of yard rakings and dirt which were absent in the
winter refuse. In addition, it contained also more
glass, food, and metallic wastes but appreciably less
paper.
b) Moisture Content of Loose
and Sacked Residential Refuse
The over-all moisture content of the winter and
spring refuse was found to vary. In the absence of
snow or rain the refuse containing yard rakings,
irrespective of whether delivered loose or in sacks,
was usually more moist than the winter refuse.
However, both types of refuse could contain dry,
moist, and wet portions.
Large differences, in moisture content between
sacked and loose refuse were found only when the
refuse was exposed to snow or rain. Both paper and
plastic sacks were found to be an effective means of
preventing precipitation from entering the refuse.
Loose refuse, on the other hand, was always found to
be affected.
Snow or light rain of short duration affected
mainly the surface portion of loose refuse. Heavy rain
or light rain of long duration raised the moisture
content of the exposed refuse to a degree where
water became the major constituent of the refuse.
samples of high food content.
The moisture content of refuse exposed to snow
was, as a rule, higher than that of dry weather refuse
only for samples in direct contact with snow.
Variations in the moisture content (see Table 11)
between 12.5 weight percent for dry refuse to 24.0
weight percent for refuse wetted by snow were
recorded.
The moisture content of loose refuse was always
high after exposure to rain. The lowest measured
value was 25 percent of total weight of the total
refuse.
However, the reported values for very wet refuse
are lower than the initial liquid content of the
delivered refuse. Higher values would have been
obtained if the total liquid content, before runoff of
excessive water, had been determined.
c) Moisture Content of Shredded Residential Wastes
One truckload of shredded refuse was received
from Madison, Wisconsin. It appeared to consist
primarily of a high proportion of shredded paper
products. However, it also contained a limited
amount of non-shredded materials such as squashed
metal cans, shoes, and rubber which were separated
during the shredding process by the Heil-Gondard
shredder, and subsequently added to the shredded
material.
34
-------
TABLE 11
Moisture in Residential Refuse
No. of
Samples
k
5
5
1
5
5
4
1
1
Dry i ng
Temp.
(°F.)
200
250
200
250
200
250
200
250
200
250
Dry i ng
Time
(hours)
16
k
16
k
21.5
11
Moisture in Percent
of Total Weight
0,0, 0,
'Q 'O 'O
Maximum
22.5
27-5
22.5
-
16
k
16
k
25.0
35.0
Mi n imum
10.0
12.5
10.0
-
17-5
15.0
250
250
250
5
5
200
250
200
250
20
18
10
16
k
16
4
22.5
~
-
12.5
~
-
Average
lit. k
16.5
17-5
17.5
Comments
Loose & Sacked
Refuse
Dry weather
(Dry, moist and
wet samples)
23.0
23.5
18.1
21.5
24.0
Loose & Sacked
Refuse. Dry
weather (moist &
wet samples)
High food content1
Loose Refuse.
Snow, (dry, moist
and wet samples)
kO.Q
50.0
25.0
35.0
28.5
kk.5
Loose Refuse.
Ra i n, s(wet" and
very wet samples)
TABLE 12
Moisture in Shredded Residential Refuse
No. of
Samples
7
Dry i ng
Temp.
( °F.)
250
Dry i ng
T ime
(hours)
7 to 20
Moisture in Percent
of Total Weight
°/
'0
Maximum
12.5
%
M i n imum
7.5
5-
'0
Average
10.7
Comments
One day
de 1 i very
35
-------
The shredded material appeared to be rather dry.
The results of the moisture determinations of seven
samples taken from the same load of shredded
household refuse are given in Table 12.
The relatively small variations in moisture
content between 7.5 and 12.5 percent of different
samples indicate a greater uniformity of the moisture
distribution in shredded than in unshredded refuse.
Moisture determinations were made with fresh as well
as stored refuse. The lowest moisture content samples
represent refuse stored over a period of days in the
test building.
2. Densities of Loose, Sacked,
and Shredded Residential Wastes
The densities of individual samples of household
refuse delivered during the period of testing varied
appreciably. Since the density of a given load of
refuse is determined both by the density of the
individual components and by the ratio of void to
occupied space in a given volume, and since both of
these factors can vary, it is not surprising that large
variations in densities can be encountered.
In order to obtain as much information as
possible about the densities of residential wastes, an
appreciable number of volume and associated weight
measurements were taken from samples of the
incoming household refuse throughout the testing
program. A summary of the computed densities of
household refuse for loose, paper-sacked, and
shredded refuse is given in Table 13.
The densities of the loose household refuse,
containing both wet and dry refuse, were found to
range from 3.8 to 15.9 pounds per cubic foot. The
lowest value, 3.8 pounds per cubic foot, was obtained
with very dry, lightweight refuse; the highest, 15.9
pounds per cubic foot, for rather wet refuse exposed
to rain.
Density values separated to reflect the effect of
moisture are shown in Table 14. They indicate that
the average density of wet refuse samples (10.5
Ibs/cuft) was about 3 pounds higher than the average
density of the dry refuse (7.6 Ibs/cuft).
The densities of the damp, spring-cleaning refuse
reflect both the presence of low density materials
such as dry leaves and dry clippings, and higher
density wet solids such as wet dirt. As a result, the
average density of the spring-cleaning refuse appears
to be more comparable to the ordinary dry refuse
than to the wet refuse which either contained a high
TABLE 13
Densities of Residential Refuse
No. of
Samples
20*4
27
3^
DENSITIES (Ibs/cuft)
Maximum
15.9
10.1
11 .0
Mi n imum
3.8
4.8
8.2
Average
9.0
7.2
9.6
COMMENTS
Household Refuse-Loose, (contained
appreciable number of samples of
high water content)
Household Refuse in Papersacks
Shredded Household Refuse (one
day del i very)
TABLE 14
Effect of Moisture on the Densities
No. of
Samples
106
12
86
DENSITIES in Ibs/cuft
Maximum
15.9
13.3
11.0
Mi nimum
7.1
5.5
3.8
Average
10.5
8.0
7.6
COMMENTS
Wet Refuse
Damp Spr ingcleani ng Refuse
(containing clippings, leaves,
and dirt)
Dry Refuse
36
-------
proportion of food wastes or was exposed to rain.
The densities of household refuse contained in
paper and plastic sacks were close to those obtained
for loose dry refuse (compare Tables 13 and 14). The
densities ranged from 4.8 to 10.1 pounds per cubit-
foot; the average density, determined for 27 samples,
was 7.2 pounds per cubic foot.
The densities of dry shredded household refuse
(Table 13). varied only between 8.2 and 1 1.0 pounds
per cubic foot. Since all samples came from the same
load of refuse, larger variations are to be expected for
samples taken over a longer period of time.
The average density of the shredded refuse was
found to be 9.6 pounds per cubic foot, 2 pounds
higher than the average value of the dry, unshredded
refuse. Since the moisture content of the shredded
refuse was low (see Table 12), and since it did not
contain a large amount of high density components,
the increase in over-all density of the shredded refuse
was associated with the reduction of void space in the
refuse.
3. Composition, Moisture Content,
and Densities of Oversized Wastes
The composition, moisture content, and densities
of oversized wastes differ from those of the other
types of household refuse. The differences in
composition arise primarily from an increased
amount of specific waste components such as metals,
wood, and textiles, and from the absence or drastic
reduction of other components such as food wastes
and papers. Although no attempts were made during
the present study to determine the properties of the
oversized wastes, it can be stated that, as a rule, the
densities of* these waste mixtures are appreciably
higher and their moisture content much lower than
that of ordinary household refuse.
II. SYNTHETIC SAMPLES OF
RESIDENTIAL WASTES
One of the major variables affecting the
properties of wastes is the continuous change of the
refuse composition. In order to eliminate this
variable, a series of experiments was made with refuse
mixtures of known composition. In addition.
synthetic samples of known composition were also
prepared to test the effect of single waste
components, such as moisture, on the compaction of
wastes. The types of samples used in the test program
were:
a) Synthetic mixtures of residential
wastes- loose
b) Synthetic mixtures of residential wastes- in
paper sacks
c) Synthetic mixtures of papers and water
d) Mixtures consisting of two components, and
e) Selected individual refuse components,
including papers, metals, glasses, rubber,
bedsprings, food wastes, ashes, and sawdust.
1. Synthetic Residential Waste Mixtures
a) Composition
Two slightly different types of synthetic
mixtures were prepared to simulate the composition
of dry household refuse. They were then placed into
paper sacks or used in the loose state and subjected to
different compaction conditions. The samples of
these mixtures were used in compaction experiments
designed to eliminate variables introduced by
different refuse compositions.
The composition of these two mixtures is given
in Table 15. The choice of the individual waste
components by type and proportion was based on
estimates of the over-all composition and moisture
content of wastes delivered by the City of Chicago
during the winter months.
Both types of mixtures contained a high
proportion of paper products, 60 percent by weight,
to simulate the high paper content of the city wastes.
The main difference with respect to the othei
components was that mixture (1) contained a few
percent more food and water than mixture (2). On
the other hand, mixture (2) contained larger amount
of contruction wastes.
In order to simulate an over-all liquid content of
dry household refuse similar to that determined from
moisture experiments with city-delivered refuse (see
Residential Refuse), liquids were either added
separately or introduced through solid wastes which
contained bound or absorbed water.
The food wastes added to the mixtures were
restricted to vegetables and fruit. These contained a
high amount of bound moisture. The following food
items were used: tomatoes, oranges, grapefruit,
lettuce, potatoes, celery, green peppers and okra.
They were partially squashed and then added to the
synthetic mixture.
b) Moisture Content
The total moisture content of the mixtures 1 and
2 was obtained by taking into account the moisture
absorbed by the solid components from the
atmosphere and the moisture subsequently
introduced by the addition of liquids and food
wastes.
Moisture in food wastes
The amount of moisture introduced through! the
addition of vegetables and fruits was estimated to be
about 80 percent of the actual weight of the food
37
-------
wastes added to the mixtures. This estimate is based Thus, it appears safe to assume that at least 80
on published data* given for the average moisture percent of the weight of the food wastes added was
content of the edible part of the wastes used in the moisture. This means that the combined moisture
synthetic mixtures: content of the mixtures due to direct water addition
Moisture and through food wastes was about 12.4 percent by
Tomatoes: 94.1% of edible portion weight for mixture (1) and about 7.8 percent by
Oranges: 87.2 " weight for mixture (2).
Grapefruit: 88.8 " Absorbed mdsture
Lettuce: 94.8 " Moisture is introduced into wastes not only by
Potatoes: 77.8 " the addition of liquids and food or garden wastes, but
Celery: 93.7 " aiso through other solid components which absorb
moisture from the atmosphere.
* Methods in Food Analysis, Maynard and Joslyn, ^n terms of moisture absorbing capabilities, paper
New York. 1950. p. 48 Academic Press Inc products rank first among the waste components
TABLE IS
Composition of Synthetic Refuse Mixtures (1) and (2)
Mixture (l)
COMPONENTS Percent of Total Weight
Newspapers
Cardboard & Corrugated Board
Junk Mai 1
Magazines
Brown Paper
Plastic Coated Papers
Tissue (absorbent)
Glass & Ceramics
Metal Cans (beer & aerosol)
Food Wastes (fruit & vegetables)
Liquids (water)
Construction Wastes (plaster,
bricks, wood)
Plastic Wastes
Text! les
Rubber
Leather
Dirt
Oi Is
18.0*
15.0
9.0
9.0
^.5
3.0
1.5
60.0%
8.0
8.0
8.0
6.0
3.5
3.5
1.0
0.5
0.5
0.5
0.5
ko.o%
Mixture (2)
Percent of Total Weight
18.0*
15.0
9.0
9.0
*».5
3.0
1.5
60.0*
8.0
8.5
6.0
3.0
8.0
3-5
1.0
0.5
0.5
0.5
0.5
ko.o%
38
-------
These products are also present in large quantities. An
estimate of the absorbed moisture introduced into
waste mixtures through exposure to a humid
atmosphere therefore has to be based primarily on a
knowledge of the absorptive properties of the papers
present in the mixtures.
In order to obtain a reasonable estimate of the
moisture in waste papers, several series of moisture
determinations were carried out during the present
study (see Table 17).
Based on these moisture determinations, it is
estimated that the absorbed moisture introduced
through papers amounts to about 10 per cent of the
weight of the paper mixture. This amount was found
to be close to the absorptive capacity of papers when
exposed to relatively dry atmospheres.
The total moisture in the synthetic mixtures (1)
and (2) (added liquids, food moisture, and absorbed
moisture in papers) is, therefore, estimated to be
about 20 and 13 per cent of the total weight,
respectively. It is, of course, clear that other refuse
items, such as textiles, also contained absorbed water.
c) Densities
The densities of the two types of synthetic
mixtures varied only slightly. The average density for
mixture (1) was found to be 7.9 pounds per cubic
foot, and 7.6 pounds per cubic foot for mixture (2).
2. Synthetic Samples of Papers and Water
A series of samples containing only paper
products and a known amount of water was prepared
to investigate the effects arising from the interaction
of moisture and papers during and after compaction.
In addition, several series of experiments were carried
out to determine the moisture contained in papers
before the addition of water.
The paper products were specifically investigated
on their own because they represent the major
component of residential wastes. Furthermore, papers
exhibit pulping and expansion characteristics in the
presence of moisture, which determine to a large
degree the compaction properties of residential waste
mixtures.
a) Composition
To investigate the influence of different degrees
of moisture on compaction, several samples of paper
mixtures and several samples containing only
newspapers were used. Newspapers were selected to
obtain information relevant to highly absorbent
papers. The composition of the paper mixtures is
shown in Table 16.
The paper mixtures were used in the compaction
experiments either after predrying or without drying.
A predetermined quantity of water was always added
to the mixture.'In total, 13 samples containing from
about 10 weight per cent to about 50 weight per cent
of water, were prepared.
Finally, 14 newspaper samples containing either
(1) loose sheets or (2) bundles of papers were also
wetted to simulate a moisture content similar to that
of the paper mixtures.
b) Absorbed moisture in papers
In addition to the water which was added to the
paper samples, some samples contained already
absorbed moisture before the introduction of water.
In view of the importance of the interaction of
moisture and papers and their large effect on
compaction, a number of experiments were made to
obtain information about moisture absorbed from the
surrounding atmosphere by the papers used. This
investigation was primarily qualitative in nature. It
was designed to provide over-all information about
moisture absorption and, together with other
information, to provide an important input for the
evaluation of the compaction process.
The moisture determinations were carried out
with samples weighing 20 pounds before drying
(individual papers) and up to 100 pounds (paper
mixtures). The papers were distributed on perforated
trays, resting on a cart which could be wheeled in and
TABLE 16
Composition of Synthetic Paper Mixture"-
Components
Newspapers
Cardboard & Corrugated Board
Junk Ma i 1
Magazi nes
Brown Paper
Plastic Coated Papers
Percent of Total Weight
39
-------
out of a gas heated oven (Dry-Sys G3 4-8 model).
In this oven, a pressure blower propelled the
heated air in a flow pattern throughout the drying
chamber, gaining access to the papers both on top of
the trays and through the bottom perforations. A
temperature controller was used to keep the
temperature constant within a few degrees for the
duration of the experiments. A low temperature of
200°F. was used during night drying periods.
However, each sample was heated in addition for at
least several hours at 250°F. during the daytime.
The paper samples were, in most cases, subjected
to drying until weight constancy within the
experimental error was achieved. Since nonprecision
TABLE
Moisture in
weighing equipment was used, and re-absorption of
water vapor during drying and weighing could not be
eliminated, the error in the moisture determinations
could have been as high as 25 percent.
The results of the moisture determinations in
different papers and paper mixtures are presented in
Table 17.
The apparent moisture content of plastic coated
papers, magazines, and cardboard was found to lie
between 2 and 5 percent of the total weight. For
newspapers, it was found to be between 4 and 26.0
weight percent, and for the paper mix, between 4.4
and 12.1 weight percent. The visual appearance of
the papers, with the exception of the newspapers
17
Papers
No. of
Samples
6
6
5
6
5
3
Dry i ng
Temp.
(°F.)
250
200
250
250
250
200
250
200
~300
Drying
Time
(hours)
3
16
9
8
3
17
3
17
2 - k
Mo is
of
*
Maximum ,
18.0
36.0
5.0
k.O
5.0
13-1
ture in Pe
Total Wei
%
Mi nimum
8.0
4.0
2.5
2.0
2.5
k.k
rcent
ght
%
Average
12.0
13.0
4.5
2.3
4.0
7-1
Comments
Newspapers
Newspapers
Plastic Coated
Papers
Magazi nes
Cardboard
Paper Mixtures (a>
(a) Paper Mixture:
Newspapers
Cardboard
Junk Mail
Magazines
Brown Paper
Plastic Coated
Weight Percentage
32.5
25.0
15.0
15.0
1.5
5.0
40
-------
containing 36 weight percent moisture, was that of
dry paper.
It should be emphasized that the moisture values
presented in Table 17 are probably lower than the
actual moisture content of the papers. In addition,
the moisture determinations were made with papers
stored for various lengths of time in a heated
building. Much higher values are to be expected for
papers exposed to high humidity.
It should also be remembered that the moisture
content of papers will be greatly affected not only by
variations in humidity but also by the various
chemical treatments given to the papers. A uniform
value of moisture for papers, therefore, cannot be
obtained even if the atmospheric conditions are kept
constant. It appears, however, that paper mixtures of
the type found in residential wastes absorb moisture
under relatively dry conditions to a level of about 10
percent or more of their weight.
3. Synthetic Samples of Papers and Adhesive
Paper mixtures of the same composition as that
given in Table 16 were also used in a short series of
tests designed to gauge the effect of adhesives on the
binding properties of wastes. Since household wastes
usually contain moisture and are largely composed of
papers, the types of adhesives chosen were water
soluble with paper adhesive properties.
Swift and Company suggested and supplied the
following adhesives:
a) Polysacharide base, 55 percent solids plus 45
percent water.
(Adhesive 45A)
b) Protein base, 55 percent solids plus 45
percent water.
(Adhesive 45C)
c) Cellulose base, 60 percent solids plus 40
percent water.
(Adhesive 45B)
d) Cellulose base, 45 percent solids plus 55
percent water.
(Adhesive 45D)
e) Jet dried blood, powder, protein base.
Another adhesive was supplied by Neville and
Company. It consisted of a hydrocarbon base
dissolved in mineral spirits (70 percent solids plus 30
percent mineral spirits).
All adhesives used in the program were further
diluted prior to application. The adhesives used with
paper mixtures contained 15 percent solids.
Adhesives used for the coating of paper sacks
contained about 20 percent of solids.
4. Selected Samples Containing One or
Several Known Refuse Components
In order to obtain information about the
compaction properties of specific refuse items of
interest, a number of experiments were made with
refuse components specially secured for this purpose.
Selected refuse components investigated on their
own, or in combination, included items such as: 1)
rubber tires, 2) bedsprings, 3) incinerator ashes, 4)
wood shavings and wood chips, 5) metal cans, 6)
refrigerators, stoves and appliances, 7) plastic scrap,
8) dry paper, 9) wood shavings and vegetables, 10)
wood shavings and meat scraps, 11) shredded rubber
and refuse, 12) wood chips and refuse, 13) oversized
wastes and refuse, and others.
SECTION THREE-COMPACTION OF REFUSE
The main objective of this part of the
experimental study was the gathering of information
and the evaluation of the compaction properties and
bale properties of different types of refuse subjected
to the same or different compaction conditions.
I. PROCEDURE
To achieve the above objectives, several series of
experiments were carried out, testing either the
influence of refuse composition or compaction
variables or both. In addition, specific variables likely
to affect the properties of the compacted refuse were
investigated on their own.
The compaction properties and properties of the
compacted bales of residential wastes were
investigated extensively. This was done in view of the
importance of acquiring realistic information, not
only about the over-all compaction properties of
household wastes, but also about the effects arising
from the continuously varying compositions
encountered in actual day-to-day operations.
To reflect different collection practices, series of
experiments were made with household refuse
delivered either 1) loose, or 2) sacked in paper or
plastic bags, and 3) with shredded refuse. They were
subjected to different compaction pressures, applied
for different time periods, and their characteristics
were determined both with respect to their properties
during pressure application and after the removal of
pressure from the compacted bales.
In addition to the experimental investigation
carried out with household refuse of random
composition, several series of experiments were also
made with synthetic samples of a predetermined
composition.
The synthetic samples were used to investigate
compaction variables on their own, and also for the
purpose of gaining information of the properties of
41
-------
specific waste components and waste mixtures.
Synthetic samples were also used.in experiments
designed to test the effect of factors such as adhesives
and moisture on the bale stability.
The synthetic samples used in the test program
consisted of mixtures- of 1) synthetic household
refuse-loose, 2) synthetic mixtures in paper sacks, 3)
water-paper mixtures containing different amounts of
moisture, and 4) different two-component mixtures
and selected refuse components of special interest.
The effects of compaction variables for both a range
of pressure and time period of pressure application
were studied with samples of the same composition.
The effects associated with the addition of special
waste components were investigated under the same
compaction conditions, using samples of successively
different compositions.
The compaction press, press operation, and
measurements of the press parameters are described
in detail in Section One of this chapter. In brief, the
individual samples of refuse were subjected to
compaction in a hydraulically operated three-stroke
press (Fig. 3). The main function of the first and
second ram of the press was the gathering of the
refuse from the large charging box into a more
confined space of about 7.8 cubic feet. The
maximum fojce which could be exerted by these two
rams was only 94 and 573 psi, respectively. The final
compaction of the refuse was accomplished by the
third ram which could exert pressure up to about
3,500 psi.
The pressure applied by the third ram was varied
during individual runs of compaction. Samples were
subjected to pressures of about 500, 750, 1,000,
1,500, 2,000, 2,500, 3,000, and 3,500 psi. Some
samples were also compacted at higher pressures,
about 6,000 psi, by concentrating the available force
of the high pressure ram on a smaller surface area. In
each case the exerted pressure of the third ram was
measured and recorded during the entire ram travel.
The equipment used provided records not only of the
applied pressure but also of the time of pressure
application as well as of the distance the ram moved
during the pressure application. The time required to
compact the bale during the final compaction (3rd
ram) was, in normal fast runs, about 17 seconds.
Initially, a number of runs were made to
determine the over-all compaction properties of the
residential wastes. The delivered wastes were
separated into different loads and their weights and
volumes were measured. These loads were then
subjected to compaction and the volume reduction in
the compaction chamber was determined as a
function of applied pressure. It was found that a
volume of about 25 cubic feet and a weight of about
200 pounds was usually necessary to produce bales of
convenient sizes. Since the standardization of the
volume was found to be less cumbersome than
standardization of the weight, most experiments were
carried out with samples of about 25 cubic feet.
However, experiments were also made with samples
of different volumes and standardized weights.
However, irrespective of whether the volume or
the weight of the uncompacted refuse was kept
constant throughout an experimental series, both the
volume and the weight were determined for any given
sample subjected to compaction. This Was necessary
in order to develop a number of important inputs
such as the densities of the incoming refuse, the
volume reduction ratios of the compacted refuse, and
the densities of the compacted bales.
The volume of the bales formed in the
compaction chamber was obtained from
measurements of the length and width of the
enclosure formed in the press by the first and second
ram after full extension, and from the determination
of the position occupied by the third ram which
provided a measure of the height of the bale (See
Section One). Since the dimensions of the enclosure
formed by the first and second ram were always
fixed, the only dimension which had to be
determined in individual runs was the height of the
bale. The dimensions, in inches, of the bale in the
compaction chamber were, therefore, in each case: 20
x 16 x variable.
The densities of the bales in the compaction
chamber were determined from weight measurements
taken after removal of the bale from the chamber,
and from determinations of the volumes of the bales
inside the compaction chamber.
Weight measurements outside the compaction
chamber were made since it was found that the
weight of the baled refuse was often less than that of
the initial load of the loose refuse. This finding
indicated that weight losses occurred during
compaction. However, the bale volume had to be
determined inside the chamber and during pressure
application since removal of pressure from the bale
always resulted in an immediate expansion of the bale
volume.
The expansion in volume of the compacted bale,
after removal from the compaction chamber, was
usually measured over a period of 24 hours and
sometimes up to 72 hours. These values were then
used to compute the densities of the bales after
removal from the press.
Further details of the experimental investigation
dealing with the compaction of wastes and the results
42
-------
obtained are given in the two following sections- II.
Compaction of Residential Wastes, and III.
Compaction of Synthetic Refuse.
II. COMPACTION OF RESIDENTIAL WASTES
In order to obtain information about the
compaction properties of wastes discarded by
households, samples prepared from different
truckloads of refuse were subjected to compaction.
Since sampling was done throughout the testing
period, it allowed an assessment of the variations to
be encountered with respect to compaction
properties in actual day-to-day operations and as a
result of seasonal changes in refuse composition.
The qualitative properties of the uncompacted
household refuse subjected to compaction have been
discussed previously in Section Two. It has to be kept
in mind that the properties of the individual samples
used in this part of the study varied from sample to
sample. However, the variations with respect to
composition and moisture content were largest for
refuse received during the two different seasons,
winter and spring, and for refuse exposed to rain as
compared to dry weather.
The experimental results are presented separately
for refuse delivered in different forms: 1) residential
refuse, loose; 2) residential refuse in paper and plastic
sacks; 3) residential refuse, shredded; and 4) oversized
wastes. This was done to highlight differences in
compaction properties other than the inherent
variations in composition originating at households,
and to emphasize the influence of collection
practices.
1. Residential Refuse—Loose
Approximately 200 different samples of loose
residential wastes were compacted during the testing
program. They contained refuse discarded by
households during winter and early spring. Their
moisture content ranged from very dry to very wet.
Some samples were covered with snow.
Different samples were subjected to pressures of
about 500, 750, 1,000, 1,500, 2,000, 2,500, 3,000,
and 3,500 psi, respectively. The decrease in volume
was measured during compaction as a function of
applied pressure. Subsequently, the expansion in
volume of the compacted bales, outside the
compaction chamber, was measured over a period of
time. The densities of the compacted refuse during
and after compaction were determined. The results of
the experimental study and the evaluation of these
results are presented in the following sections.
a) Volume Reduction During Compaction
The reduction in volume by compaction was
accomplished in several steps. Initially, any given load
of refuse was gathered by the first ram of the press
into a space occupying 23.3 cubic feet. Subsequently,
the volume of the refuse was reduced to about 7.8
cubic feet by the action of the second ram of the
press. The final compaction from 7.8 cubic feet to its
lowest volume was then accomplished by the
advancement of the high pressure ram which confined
the refuse into a bale of the dimensions of 20 x 16 x
variable inches. The only variable dimension (height
of the bale) was determined in each experiment from
electronic measurements of the third ram deflection.
An example of the recorded third ram deflections
as a function of applied pressure, and the respective
change in bale height, is shown in Figure 9. The upper
curve was obtained with eight different samples
prepared from the same load of refuse, each weighing
200 pounds, which were compacted at different
pressures. It can be seen that the superimposed curves
of the individual runs coincide above a pressure of
about 1,000 psi, indicating the great similarity in
properties of the individual samples. Differences in
curvature below 1,000 psi, however, show that the
compressibility of the samples was not the same over
the whole range of pressure. The lower curve in
Figure 9 shows the ram deflection of a sample of
greater weight.
Curves which could not be superimposed were
obtained for equal weight samples prepared from
loads of refuse of different properties. However, the
composite curve in Figure 9 represents a good
example of the over-all change in bale height and
therefore in bale volume of individual samples of
both similar and different properties. For example,
the bale height always decreased with an increase in
unit pressure over the whole pressure region tested.
The decrease was also always more pronounced in the
region below 1,000 psi than above 1,000 psi.
As mentioned previously, experiments were
carried out with samples constant in either volume or
weight. In addition, experiments were made with
samples of different volume and weight. Variations in
volume of the uncompacted refuse ranged from about
15 to 45 cubic feet, and in weight from about 130 to
400 pounds.
In most cases the volume of bales in the
compaction chamber-, when compacted at 3,500 psi
from an initial load of 25 cubic feet, was found ta be
in the region of 1.6 to 2.6 cubic feet. The largest bale
of about 4.0 cubic feet was produced from a
45-cubic foot sample. The smallest bale, 1.1 cubic
feet, was obtained from a load of about 25 cubic feet.
The volume reduction ratios of different types of
refuse subjected to the same pressure varied from
about 7:1 to about 23:1. Volume reduction ratios
43
-------
30 •
o
c
.- 20 "
c
o
o
-------
TABLE 19
Volume Reduction Ratios of Different Bales Compacted at
Different Pressures
No. of
Samples
15
27
8
13
Maximum
15-0 : 1
17.7 : 1
13-5 : 1
12.0 : 1
Mi nimum
6.3 : 1
6.8 : 1
7.2 : 1
7.0 : 1
Average
9.1 : 1
11 .6 : 1
9-7 : 1
8.9 : 1
Compact ion
Pressure (psi)
2300 - 2500
1850 - 2000
1400 - 1500
850 - 1000
TABLE 20
Volume Reduction Ratios of LooSe Household Refuse as a
Function of Incoming Densities and Compaction Pressures
Samples
31
29
14
28
3
5
8
13
Densi ties
of Loose Refuse
(averages in Ibs/cuft)
6.7
10.8
6.9
10.8
6.8
10.6
7.6
10.0
Volume Reduction
Ratios
(averages)
15.0 1
9.1 1
13.2 1
9.5 1
12.0 1
8.3 1
9.8 1
8.1 1
Compaction
Pressure (psi)
3000 - 3500
1850 - 2500
1350 - 1500
650 - 1000
either with differences in initial void space or
compressibility of the components in a given refuse
load.
In cases in which the solid items in the refuse are
more difficult to compact, it is to be expected that
the remaining void space in the compacted bale is
larger than in bales produced at the same pressure
from refuse loads which can be easily compacted.
Variations in void space left in the bales could
account, therefore, for differences in the volume of
the refuse bales. However, the differences in void
space left in the compacted household refuse were
generally much too low to be able to account for the
large variations in volume reduction. On the other
hand, large variations were observed in initial void
space of the loose refuse. These, therefore, could
more easily account for the differences found in the
reduction ratios of different refuse samples.
The densities of loose refuse samples containing
materials of similar densities but varying amounts of
voids should vary in direct proportion to the
contained void space. Similarly, the volume reduction
ratios of samples containing materials of comparable
compaction properties should vary with void space. It
is .to be expected, therefore, that a direct
proportionality between incoming densities and
volume reduction ratios will be found in all cases in
which the difference between the refuse samples is
based only on a varying amount of void space.
In order to test whether differences in void space
are responsible for the differences found in the
reduction ratios, an attempt was made to determine
the relationship between the densities of the
uncompacted refuse (see Section Two) and the
volume redaction achieved by compaction. The
results of this evaluation are presented in Table 20.
The low density values of 6.7 to 7.6 are averages
for loads which had densities in the range of 3.6 to
8.0 pounds per cubic, foot. The high values of 10.0 to
10.8 are averages for loads having loose densities in
45
-------
the range between 8.0 and 15.9 pounds per cubic
foot.
It can be seen that the reduction in volume of the
low density refuse was higher than the volume
reduction of the high density refuse, irrespective of
the pressure applied. The average volume reduction of
the high density refuse varied at different pressure
only between 8.1 and 9.5 whereas the volume
reduction of the low density refuse varied from 9.8 to
15.0. The difference in the magnitude of the volume
reduction ratios for low and high density refuse was
more pronounced at pressures above 1,000 psi.
The interrelationship between the densities of the
loose refuse and the associated volume reduction
ratios appears to be quite striking. For example, at
3,500 psi, the increase in density by a factor of about
1.61-from 6.7 to 10.8 pounds per cubic foot (first
row of Table 20)—was accompanied by a nearly
equivalent decrease in the volume reduction ratio
from 15 to 9.1. In the other pressure ranges above
1,000 psi, an increase by a factor of about 1.6 in
density was accompanied by a simultaneous decrease
by a factor of about 1.4 in the volume reduction
ratios; below 1,000 psi, the increase in density by a
factor of 1.3 led to a decrease in the reduction ratio
by a factor of 1.2.
The data suggest that the average decrease in
volume to be expected at pressures above 2,000 psi is
likely to be about 14:1 for loose household refuse of
densities in the vicinity of about 6.8 pounds per cubic
foot and about 9.3:1 for loose refuse of a density of
about 10.8 pounds per cubic foot.
The observed relationship between the loose
densities and the reduction in volume suggest strongly
that the main difference between different refuse
samples of residential wastes is that some samples
contain a larger proportion of voids than others.
However, since the increase in density, was not
always accompanied by a corresponding increase in
bale volume it is clear that the material properties of
the refuse also affect the reduction in volume, but to
a lesser degree.
Based on the data given in Table 20, it is
expected that a 100 percent increase in density of
the loose refuse may be accompanied by a decrease in
bale volume of about 70 to 90 percent.
c) Changes in Volume and Bale Formation
During Final Compaction
The changes in volume d«iag.the final stage of
compaction were found to be, in all cases, much
smaller than in the early stages of compaction. During
the early stages which utilized only the first and
second low pressure rams, the reduction in volume,
however, did not lead to the production of a stable
bale structure. Similarly, the reduction in volume
accomplished during the last stage by the movement
of the third high pressure ram usually did not
produce cohesive bales below 1,000 psi.
The most effective pressure range for the
formation of cohesive bales was usually above 1,000
psi; furthermore, the stability of the bales was
enhanced as the pressure increased.
In view of the importance of the final volume
decrease during which the materials in the refuse are
brought together into close contact, the relationships
between volume decrease of different samples as a
function of applied pressure were evaluated.
The change in volume during final compaction of
four 25-cubic foot refuse loads of different loose
densities in the pressure range of 500 to 3,450 psi are
shown in Figure 10.
The results presented in Figure 10 show that the
final volume obtained at about 3,500 psi differs for
the two sets of refuse loads each of which occupied
initially 25 cubic feet, and that the initial density had
a marked effect on the ultimately achieved volume
reduction. Refuse samples of loose densities of 10.2
and 11.2 (curves 1 and 2) produced larger bales than
refuse samples of loose densities of 5.2 and 5.4
(curves 3 and 4);(curve 3) the volume-pressure curves>
of samples of initially similar densities coincided at
high pressures but showed differences at lower
pressures. In addition, both low and high density
samples produced steeper and shallower curves,
indicating inherent differences in refuse properties
other than the void space in the refuse. The volume
decrease in the pressure range between 1,000 and
3,500 psi was about 1.1 to 1.3 that of the volume of
the samples at 1,000 psi. In comparison, the volume
of the initial loads decreased by a factor of 8.0 to
about 14.0 during compaction up to 1,000 psi. This
demonstrates clearly that compaction in the higher
pressure region does not lead to a large decrease in
volume. Its value lies in the fact that a very close
contact between the solids in the refuse improves the
stability of the compacted refuse.
The curves in Figure 10 show that close contact
between the solids was achieved for different samples
at different pressures: Nearly all voids were already
expelled from the refuse sample (4) at about 2,000
psi, whereas a pressure of about 3,000 psi was needed
to reduce the volume of the other samples to achieve
a similar result.
As mentioned before, the stability of the
individual compacted bales was found to be improved
after compaction at higher pressures. However, an
improvement in stability was also found if the
46
-------
_Q
3
ene:> ol experiments wa:> nude lo ilud> Uie
effect of pressure holding time on the properties of
compacted bales. This was done to determine
whether holding of pressure can be used to reduce the
internal expansion forces created in the bales during
compaction and whether time could be used as a
substitute for higher pressures.
It was found that holding of pressure during
compaction always led to a decrease in bale volume.
This observation indicated clearly that the internal
expansion forces created in the refuse during
compaction can be partially overcome by applying
pressure for a longer time. This effect indicated that
the refuse behaved as a semi-elastic material. The
main refuse components responsible for its over-all
springback characteristics were most likely paper
products. Papers, which are made up of fibers, tend
to spring back after release of applied pressure if the
fibers are only bent during pressure application.
Higher pressures or application of pressure for a
longer time, however, can weaken the bonds in the
bent fibers and, therefore, reduce the springback
force.
The large expansion forces created in the bales
during compaction can be observed immediately after
removal of the pressure from the compacted bale.
Due to the operation of the compaction press used in
the tests, the pressure was removed initially from the
461-084 O - 72 - 5
47
-------
third high pressure-ram. At this time the second and
first rams were still locked in position and, therefore,
the expansion occurred only in the height direction.
Subsequently, the bale expanded also in the other
two directions, after release of the other two rams.
To determine the magnitude of the expansion in
height, recordings of the ram extension-pressure
curves taken during different experiments were
evaluated. It was found that expansions in height of
about 20 percent occurred in many cases within 1 or
2 seconds after pressure release.
A demonstration of the high expansion forces
produced in the compacted bales of residential wastes
is given in Figure 11. It shows a sequence of third ram
deflections for a bale of refuse initially compacted at
3,500 psi and then three times at lower pressures. In
this experiment the high pressure ram was retracted
to its original zero position after each pressure
application. The calculated height of the bale at
3,500 psi (curve "a") was found to be 12.25 inches.
After release of pressure, it was found that the bale
height increased by about 30 percent (see origin of
curve "b"). Pressure had to be applied again to
decrease the volume of the expanded bale. Even after
a pressure of 1,150 psi was exerted three successive
times (curves "b", "c" and "d") to the bale originally
compacted at 3,500 psi, the bale height did not
decrease to the value attained during the first
compaction. This experiment shows that the internal
pressure developed at 3,500 psi was greater than
1,150 psi. However, it also shows that the successive
application of pressure led to a decrease in
subsequent expansion (compare origin of "a", "b",
"c" and "d").
The effect of pressure holding time on bale
volume is shown in Figure 12. It can be seen that
holding of pressure was quite successful in
overcoming part of the counterforces initially
developed in the bales. Curve "a" shows the decrease
in bale height with time of a bale compacted
sucessively at increasing pressures for 5 minutes.
Curve "b" shows the results obtained with six
different refuse samples prepared from the same
refuse load. The smooth curve, up to about 2000 psi,
represents the change in bale height of two fast runs.
Holding of pressure for either 5 or 10 minutes at
about 1,000, 1,500 and 2,000 psi led to the same
pronounced decrease in bale volume. Curve "c"
shows the decrease in bale height at about 1,000 psi
with time of pressure application, and the subsequent
decrease after raising the pressure to about 3,500 psi.
The latter result indicates that the reduction in
volume with time at low pressures is not of the same
magnitude as that which can be achieved at the
highest pressures in fast runs.
The results obtained with residential wastes,
loose or sacked, and also those obtained with
synthetic samples of residential wastes, all showed
that the maximum decrease in bale volume with time
was achieved at low pressures. In the region of about
1,000 psi and up to approximately 1,700 psi the
decrease in bale height was usually about 1 inch.
In addition, evaluation of the recordings of the
changes in ram deflection with time indicated that
the maximum decrease was reached after less than 1
minute of pressure application. This means that the
optimum volume decrease in the baler can be most
likely achieved by applying pressure for about 15 to
30 seconds and that the effectiveness with respect to
the volume change is highest in the low pressure
region.
e) Bale Densities During High Pressure Compaction
The result of the reduction in volume achieved
by compaction is an increase in the density of the
compacted refuse. This increase is directly
proportional to the volume decrease. Since the
volume decrease, with increase in pressure, is more
rapid at pressures below 1,000 psi, the density also
increases more rapidly in this pressure region.
The densities of the refuse gathered by the first
and second ram into a space of about 7.8 cubic feet
before final compaction ranged from about 12 to 50
pounds per cubic foot, a variation of about 400
percent. The average density of the 204 refuse
samples was, at this stage, about 29 pounds. This
includes both wet and dry refuse loads
The densities of the compacted household refuse
during final compaction, computed for samples
subjected to different pressures, are presented in
Table 21.
The results in Table 21 show that the average
density of the compacted bales of household refuse
was about 90 to 93 pounds per cubic foot at
pressures above 1,850 and up to 3,500 psi. The
differences in the densities of individual bales in this
pressure region were found to be about ± percent of
the average density.
Generally, lower values were obtained after
compaction at lower pressures. However, similar
values were found in different pressure regions.
An important result shown in Table 21 is the
-apparent lack of effect of the density of the incoming
refuse on the ultimately achievable density of the
compacted bale. This result seems to be in accordance
with the previously made observation (see section b)
that on the average, the density of the loose refuse
varied primarily as a result of differences in void
space within the refuse. It also implies that both wet
48
-------
0)
O
a = fi rst compaction
e
fD
a:
20
r ,
500
1500
2500
3500
Ram Pressure in psi
FIGURE 11
Residential Waste. Sequence of Ram Deflections for
Loose Refuse Compacted Initially Up to 3500 psi (a)
and then at 1150 psi (b, c, d)
-------
TABLE 21
Densities of Bales of Residential Refuse, as a Function of
Incoming Densities and Compaction Pressure
No. of
Samples
31
29
14
28
3
5
8
13
Average
Dens i t ies of
Loose Refuse
(Ibs/cuft)
6.7
10.8
6.9
10.8
6.8
10.6
7.6
10.0
Densities of Bales
(Ibs/cuft)
Average
93
93
90
90
82
86
7k
7k
Maximum
108
102
104
103
86
95
77
90
M i n imum
78
78
82
84
77
83
70
66
Compact i on
Pressure
(psi)
3000 - 3500
1850 - 2500
1350 - 1500
650 - 1000
and dry refuse loads contained either solid
constituents of higher and lower densities in similar
proportions, .or that the proportion of one or a few
constituents was so predominant in each compacted
mixture that the over-all density was not appreciably
affected by the introduction of moisture or items of
very different densities. Since the main constituents
of the household refuse received during the present
program were usually paper products, it is likely that
their presence in large quantities was responsible for
the relatively uniform distribution of densities of
different samples.
The densities of 78 pounds per cubic foot and
108 pounds per cubic foot, obtained for samples
compacted at high pressures, suggest that the portion
made up of items other than papers contain primarily
higher density items than dry papers. This conclusion
is based on the fact that the densities of different
types of papers lie between 43 and 71 pounds per
cubic foot, therefore, the density of a mixture of
papers and similar density materials should not
exceed a value of 71 pounds per cubic foot. On the
other hand, higher density components, and also wet
paper products should lead to a higher over-all
density.
It was originally expected that compaction of
very wet refuse would produce bales of appreciably
higher densities than those found. However,
experiments conducted with paper-water mixtures
(see Section II) showed that the difference in
densities between paper mixtures containing about 10
and 50 weight percent of water was not more than
about 20 pounds per cubic foot. This was due to the
partial release of moisture during compaction and
also to the swelling of very wet papers which
therefore occupied a larger volume than dry papers.
As mentioned before, variations in the incoming
densities of different refuse loads had little effect on
the density of the compacted bales. These variations,
however, did have an appreciable effect on the
volume reduction ratio. As a result, refuse samples of
the same volume produced bales of a large variety of
sizes, whereas samples of the same weight produced
bales of similar sizes. This finding suggests that
control of the weight of the incoming refuse provides
a better means for the control of the compacted bale
si/e
In order to determine the relationship between
weight input and size of the bales, the volumes
initially obtained for refuse loads of different weights
were recalculated to reflect constant loads of 200
pounds. The results (Table 22) show that the average
volume occupied by 200 pounds of residential wastes
was about 2.04 cubic feet at high pressure and that
the variations in volume were approximately ± 15
percent of the average volume. This means that 100
pounds of loose refuse produced bales of about 1.02
cubic feet on the average. The experimentally
determined relationship found between incoming
loose weight, compaction volume and bale density at
high pressure was:
100 Ibs - 1.02 ± 15%/cuft - 93 ± 15% Ibs/cuft
On the basis ol the results presented in Table 22
it would be expected that the average densities of the
bales should have been about 98 pounds per cubic
50
-------
TABLE 22
Volume of Bales Compacted at 3000 to 3500 Psi
for loads of 200 Pounds Loose Refuse
No. of
Samples
60
Weight of
Loose Refuse
(Ibs)
200
Volume in
Compaction Chamber (cuft)
Maximum
2.3
Mi n imum
1.8
Average
2.0**
Compaction
Pressure
(psi)
3000 - 3500
foot. However, the measured densities were found to
be lower, indicating that weight losses occurred
during compaction.
f) Weight Losses During Compaction
In most cases it was tound that the weight of the
bales, measured after removal from the press, was less
than the weight of the loose charge placed in the
baler.
The loss in weight was in part due to spillage of
loosely adhering solids from the bale, and to loss of
material which remained in the small openings
between the moving parts of the press. However,
these losses accounted only in part for the difference
in incoming and outgoing weight of the refuse
Weight losses which occurred during compaction
arose mainly from liquid and liquid-solid suspension
losses. These losses were always highest when the
loose refuse was very wet. Weight losses of up to 37
weight percent were recorded for refuse exposed to
rain. Moderately wet refuse usually lost only 1 to 3
percent of its initial weight. Liquid losses do not
occur during compaction of dry refuse.
The average weight loss of about 5 percent in the
density values (see previous section) was larger than
the loss expected to occur during compaction.
However, it has to be remembered that an appreciable
number of bales compacted during the testing
program contained liquids in excess of the liquids
usually introduced by households. Some of the wet
loose refuse was exposed to ram and snow, other
contained moist yard rakings. Since the density values
were obtained from samples ranging from very wet to
very dry, and since most samples were either moist or
wet, a relatively high loss was recorded, reflecting the
seasonal influences of winter and early spring.
The gathering and disposal of the extracted liquid
has to be considered in the design of a compaction
station. Uncontrolled seepage of leachings around the
press and their disposal could introduce pollution
hazards which have to be avoided. However, in order
to identify the measures required to control this
condition, it is necessary to evaluate the pollution
properties of the leachings.
g) Properties of Leachings Released
During Compaction
An attempt was made to obtain information of
the chemical and microbiological properties of the
leachings released during compaction. For this
purpose a tray was installed below the compaction
area of the press and the leachings were collected and
later analyzed.
Leachings were collected for the chemical
analysis over a period of about two weeks, since the
released amounts were quite small at the time of
collection. It should be emphasized that appreciable
amounts of leachings are only to be expected if the
refuse is wet, which was not the case for most
samples compacted at the time in question. About
2.0 liters of the collected leachings were submitted
for analysis.
The collection of leachings for the
microbiological analysis had to be carried out in a few
hours to avoid changes in properties induced by time,
and to allow analysis of some of the constituents
within a few hours of collection. In order to obtain a
large enough sample in such a short period, water was
added to the refuse before compaction. A sample of
about 1.5 liters was ultimately obtained.
Precautions were taken to keep the leachings for
the microbiological analysis at low temperatures
during collection and transport to the laboratory by
immersing the collection bottles in ice. Arrangements
were made to carry out part of the microbiological
analysis the same day of collection, immediately on
arrival of the samples.
The chemical analyses were undertaken by the
analytical personnel of the City of Chicago Testing
and Inspection Division. The microbiological analyses
were carried out by the personnel of the City of
Chicago Board of Health. The results submitted by
these two laboratories are given in Tables 23 and 24.
The chemical analysis of two different samples
was made after separating each sample into two
portions, one containing the liquid and the other the
sludge portion of the samples. However, the liquid
portion also contained suspended solids.
51
-------
The color of the sludge was light gray, and the
color of the liquid was greenish in appearance. The
odor of both samples was quite offensive.
The results m Table 23 show that both samples
contained the same types of constituents. However,
the concentrations of the individual constituents
varied with the sample.
The main difference in composition of the sludge
of the two samples was thai Sample. I contained a
higher percentage of all constituents with the
exception of organic matter. Nevertheless, in both
cases the main portion of the sludge was organic. The
concentration of organic matter in the liquid portion
of tjie samples was also higher in Sample 2 than in
Sample 1.
The high percentage of organic matter found in
the sludge is to be expected since refuse contains a
large proportion of organic constituents. It could
have contained cellulosics from the paper products,
and other organics from different manufactured and
natural products, especially those found in food and
garden wastes.
The inorganic constituents of the sludge—silica,
aluminum, calcium, magnesium, and iron-are likely
to have been introduced through soil, vacuum cleaner
catch, crushed glasses, and ceramics. The percentage
of these. constituents in soil and dirt is about 59
percent Si02; 15 percent A1203; 5 percent CaO and
3 percent Fe203. A mixture of these types of
products could readily account for the respective
percentages of the individual components found in
the chemical analysis. It is, therefore, unlikely that
they present any pollution hazard. Only traces of
sulphates and no carbonates were found in the sludge.
However, an appreciable amount of phosphates was
detected in both samples.
The liquid portions of the two Camples were
found to be distinctly different with respect to their
pH. Sample 1 was slightly alkaline; Sample 2 was, on
the other hand, acidic. A different sample submitted
at a later stage for analysis to the Board of Health had
a pH of 7, indicating that the leaching in this case was
neutral.
The acid sample contained a higher proportion of
TABLE 23
Chemical Analysis of teachings
SLUDGE
Organic Matter
S i 1 i ca as Si 0.
Aluminum as Al 0
Phosphates as P.O
Ca Icium as CaO
Magnes ium as MgO
Iron as Fe-0,
Sulphates as SO.
Carbonates as CO
L 1 QU 1 D
PH
Total dissolved solids
Organic Matter
Bicarbonates
Su 1 phates
Chlor ides
Heavy metals (suspension)
Sample 1
38.9%
30.8
15.2
8.9
2.0
1.4
0.5
Trace
0.0
7.8
6090 ppm
1720
90
250
21
Large % amount
Sample 2
76.72
6.9
5.8
4.4
1.3
0.0
0.6
Trace
0.0
4.5
6040 ppm
4480
610
200
218
Smal 1 % amount
52
-------
bicarbonates and chlorides than the alkaline sample.
The bicarbonate content of the acidic sample appears,
however, to be higher than would be expected for an
acid solution of the given strength. Normally,
carbonates are expelled out of the liquid in the form
of C02 when subjected to relatively weak acids.
As tound with the sludge, the liquid portion oi
Sample 2 contained a higher amount of organic
matter and a smaller amount of suspended metallics
than the liquid portion of Sample 1. The amount of
the total dissolved solids was about the same in both
cases; the amount was relatively high. It has to be
remembered, however, that the samples submitted for
analysis were concentrated solutions of high sludge
content collected over a longer period of time.
The microbiological findings presented in Table
24 show that no pathogenic microorganisms, with the
exception of one virus, were detected in the
leachings. This is not surprising since many
pathogenes cannot survive outside a living host
organism for any length of time.
Most of the identified bacteria were found to be
bacterial spores. Since it is commonly recognized that
bacterial spores are more resistant in their capacity to
withstand external destruction, it is not surprising
that they are part of the population of
microorganisms found in refuse.
The aerobic and anaerobic plate counts indicate
that both aerobes and anaerobes were present in
about equal numbers. Their numbers were quite high.
The coliform group and fecal strep counts were also
high. Since a fecal coliform test was not run, it is not
clear whether the strep count can be used as an
adequate indicator of fecal contamination.
It is not surprising that the leachings contained
an appreciable amount of some of the pollutants,
especially since both the chemical and biological tests
were carried out with concentrated samples designed
primarily to allow detection of the type of pollutants
which could be encountered in the refuse. It should
also be remembered that the investigation was
restricted to a few tests and that a more quantitative
study would be required to assess the pollution
potential of the leachings. The findings, however,
show the promise of the approach and the great
desirability of an expanded systematic program which
would be to the benefit of the whole solid-waste
disposal field.
With respect to compaction, however, it has to be
emphasized that the chemical and microbiological
constituents detected in the leachate were not
introduced into the refuse by the compaction
process. These constituents are part of the normal
makeup of solid wastes disposed of m everyday
operations. Since some of the pollutants are extracted
from the wastes during compaction, the compacted
wastes should, in fact, contain fewer contaminants
than the wastes entering the compaction plant.
h) Volume Expansion of Bales After Compaction
Ihe volume ol each compacted refuse sample was
found to increase immediately after removal of the
compaction pressure. Initially, the expansion inside
the baler occurred only in the height direction since
the two lower pressure rams were locked into
position and therefore prevented expansion into the
length and width direction. It was, however, quite
apparent that a three-dimensional expansion of the
bale would have occurred if the freedom of expansion
had not been restricted. In fact, it was found
necessary to unlock the low pressure rams and allow a
three-dimensional expansion in order to remove the
bales from the compaction chamber without
destruction. Nevertheless, the expansion in height was
always more pronounced than in the other directions.
The expansion of the bales outside the
compaction chamber was measured at predetermined
time intervals. The rate of increase was found to be
largest, in all cases, immediately after compaction was
completed. However, the bale volume increased at a
slower rate over a long period.
Measurements taken 1 to 2 minutes after
completion of compaction showed that the volume
expansion during that time amounted to about 50 to
60 percent of the original compacted volume. The
computed values of the volume expansion occurring
during 1 to 2 minutes for samples compacted at
different pressures in fast runs (without holding of
pressure) are given in Table 25.
The average volume increase of the samples of
lower loose densities was slightly higher than the
volume increase of the higher density samples.
However, large variations in volume expansions were
recorded for individual samples.
An accurate determination of the volume of the
expanded bales was not possible. The .expansion
forces acting within the bale were found to be
non-uniform. This non-uniformity led to the
formation of distorted bales and prevented accurate
volume determinations. The distortion of the bales
was always highest for those compacted at lower
pressures. The least distortion occurred after
compaction at about 3,500 psi. An improvement was
also found for bales compacted at lower pressures, if
the pressure was applied for a period of time.
As a rule the expansion in volume within 1 to 2
minutes after release of pressure from the bale was in
the region indicated in Table 25. Variations in volume
expansion of the different bales were in the range of
53
-------
TABLE 24
Microbiological Analysis of teachings
A. BACTERIOLOGY
Aerobic plate count
Anaerobic plate count
Identified Bacteria (to genus)
Yeasts
Molds
B. PARAS ITOLOGY
C. WATER BACTERIOLOGY
1. Standard plate count @ 35°C:
2. MPN technique:
3. Fecal streptococci (membrane fi
*». Staphylococci (membrane filter)
D. VIROLOGY
E. CHEMISTRY
8.3 x 10 organisms/ml.
7-7 x 10 organisms/ml.
1 . Baci 1 lus sp.
2 . Col i form group
3. Proteus sp.
b. Streptococcus sp.
(a Ipha hemolyt ic and
non-hemolyt ic noted.)
5- Alcal igenes sp.
6. Micrococcus sp.
(coagulese negative)
7. Flavobacter sp.
8. Aerobacter sp.
Yeast cells were observed.
1 . Penici 1 1 ium
2. Streptomyces
3 . Paeci lomyces
k. Mucor
A number of free living amoebae
as we?] as cMiates were noted.
k .9 x 10 organisms/ml.
Q
9.2 x 10 organisms per 100 ml.
lter):7.0 x 10 organisms per 100 ml.
: 5-7 x 10 organisms per 100 ml.
Virus isolated and identified as
ECHO by anti-serum neutraliza-
tion.
pH: 7; D.O.: none
54
-------
about 25 to 90 percent.
Bales made from refuse containing snow
developed an ice cover which inhibited bale growth
within the first expansion period. The expansion of
these bales was usually not more than 25 volume
percent. High values, however, were obtained for
individual samples of both very dry and very wet
refuse. The high values probably resulted from the
high springback forces of bent paper fibers when dry,
and also from swelling effects of paper materials
when wet.
The expansion ol bales occurred prelerentially.
In all cases the expansion of bales compacted at high
pressures was substantially greater in the direction of
the bale height. For example, for a bale whose
over-all volume increased about 60 percent, the
height increased by about 50 percent , and the length
and width about 4 and 2 percent, respectively. As a
rule the expansion in length was greater than in
width.
The preferential expansion of the bales followed
the sequence of the three-step compaction process:
least expansion occurred in the direction of the
lowest pressure application, first ram movement; and
the maximum expansion occurred in the direction of
the highest pressure, third ram movement.
The respective order of expansion m the three
pressure directions remained always the same,
irrespective of the properties of the compacted
refuse. However, if the refuse was wet or if the refuse
was compacted at lower pressures, the degree of the
expansion in width and length was higher. The
maximum increase after 1 or 2 minutes was about 20
percent in length and about 10 percent in width.
The volume of bales after 24 to 72 hours was
always larger than after the first few minutes. Bales
stored individually and left to expand without any
restriction, grew up to 95 percent larger than their
original compacted volume.
The computed volume reduction ratios after
volume expansions are also given in Table 25. The
effect of loose densities on the volume reduction
ratios found for the refuse during compaction (see
Table 20) was found to be present after volume
expansion. The variations in volume reduction ratios
ranged between 5.1 and 6.4 for high density samples
and between 6.6 and 10.0 for the low density
samples.
Placement of bales into close proximity, next to
each other and on top of each other, could reduce the
over-all growth either in one or all directions
depending on the stacking procedure adopted.
However, additional work is nefeded before a definite
assessment can be made of the influence of stacking
on bale growth
i) Densities of Bales After Volume Expansion
I he direct consequence ol the expansion of the
bales is a reduction in the densities of the bales. The
densities of the bales after initial expansion are given
in Table 26.
It can be seen that the average densities of the
bales compacted at 3,000 to 3,500 psi were about 61
to 65.5 pounds per cubic foot after expansion took
place. These values are found to be about 30 percent
lower than the values obtained during 'compaction
(Fig. 13). The maximum decrease in density (about
37 percent ) appeared to occur with bales compacted
at 1,350 to 1,500 psi.
TABLE 25
Volume Expansion of Bales After Compaction
No. of
Samples
31
29
14
28
3
5
8
13
Average
Loose Densities
(Ibs/cuft)
6.7
10.8
6.9
10.8
6.8
10.6
7.6
10.0
Average
Volume %
\ ncrease after
1 to 2 Min.
50%
43
66%
56
62%
51
49%
59
Volume Reduction
Ratios after
1 to 2 Min.
10.0 1
6.4 1
7-9 1
6.1 1
7.4 1
5.5 1
6.6 1
5.1 1
Compact ion
Pressure
(psi)
3000 - 3500
1850 - 2500
1350 - 1500
650 - 1000
55
-------
The data in Table 26 show a distinction between
the densities of bales compacted above and below
1,850 psi. The density values of the bales compacted
above 1,850 are all close to 60 pounds per cubic foot.
whereas those below that pressure have values close
to 50 pounds per cubic foot. The differences between
the densities of the samples of initially high and low
loose densities is found to be slight.
TABLE
Densities of Bales after
j) Effect of Pressure, Pressure Holding Time and
Moisture Content on the Stability of Bales After
Compaction
Several iactors were found to affect the stability
of the compacted bales of residential wastes. The
major factors were compaction pressure, time of
pressure application, and the moisture content of the
wastes.
26
Volume Expansion
No. of
Samples
31
29
1*
28
3
5
8
13
Average
Densities of
Loose Refuse
(Ibs/cuft)
6.7
10.8
6.9
10.8
6.8
10.6
7.6
10.0
Average
Densities of Bales
After 1 to 2 Min.
Volume Expansion
(Ibs/cuft)
61
65.5
58.5
60.0
50
5**
49-5
W.Q
Compaction
Pressure
(psi)
3000 - 3500
1850 - 2500
1350 - 1500
850 - 1000
90
70
« 50
30
During Compaction
After Volume Expansion
500
1500
2500
3500
Ram Pressure in psi
FIGURE 13
Average Densities of Residential Wastes
During and After Compaction
56
-------
In the absence of excessive moisture, compaction
at high pressures resulted in the formation of stable
bales. On the other hand, bales compacted at low
pressures were quite fragile.
Fragile bales were usually obtained after
compaction at pressures between about 500 to 1,000
psi. These bales occasionally fell apart immediately
after removal from the baler. Some fell apart after
being handled successively several times. An
improvement in stability was found for bales
compacted at pressures between 1,000 and 1,500 p^i.
However, the stability of most bales was markedly
improved after compaction at 2,000 psi and up to
3,500 psi. A further increase in pressure, up to 6,000
psi, produced no apparent improvement in bale
stability.
The over-all stability of the bales compacted at
about 1,000 and 1,500 psi usually improved
appreciably if the force on the bales was held for
several minutes (see Part "d"). The bales compacted
at about 1,000 psi for 5 minutes seemed to be stable
as those compacted at 1,500 to 1,750 psi without
holding of pressure. Similarly, the bales compacted at
about 1,500 psi for 5 minutes appeared to have the
properties of samples compacted at about 2,000 psi
without holding of pressure.
The stability ol bales ot very high moisture
content was always poor, irrespective of the
compaction pressure applied. There were, however,
indications that tne stability of the bales containing
an appreciable amount of moisture could be
improved if the compaction pressure were lowered.
2. Paper-sacked and Plastic-sacked Residential Wastes
The composition, moisture content, and densities
of the uncompacted paper- and plastic-sacked refuse
were discussed previously (see Section Two). The
over-all properties of the refuse inside the sacks were
similar to those of the loosely delivered refuse, the
main difference being that moisture content of the
refuse in the sacks remained largely unaffected by
external influences such as rain and snow. This meant
that the adverse effects, introduced into the loose
refuse by rain, were eliminated. The only other
significant difference between the sacked and loose
refuse was the presence of the sack itself. The
TABLE 27
Volume Reduction Ratios of Paper^and Plastic Sacked
Residential Wastes During Compaction
Densities of the
Uncompacted Refuse
(Ibs/cuft)
Maximum
10.1
9-7
Mi nimum
k.B
6.3
Average
7.^
7.7
Volume Reduction Ratios
Maximum
17 : 1
13 : 1
Minimum
9 : 1
9 : 1
Average
13 = 1
11 : 1
Compact ion
Pressure
(psi)
3300 - 3500
1850 - 2000
TABLE 28
Densities of Bales of Paper—and Plastic Sacked Refuse
During Compaction
Densities of the
Uncompacted Refuse
(Ibs/cuft)
Maximum
10.1
9.7
M i n imum
it. 8
6.3
Precompacted at
3500 psi
Average
7. A
7.7
69.75
Densities of Bales
(Ibs/cuft)
Maximum
106
93
70
M i nimum
90
81
69
Average
9^
85
69-5
Compact ion
Pressure
(psi)
3300 - 3500
1850 - 2000
6000*
2 bales only
57
-------
compaction results and the effect of the enclosure are
discussed below.
a) Volume Reduction During Compaction
Ihe over-all change in volume oi sacked refuse
with compaction pressure followed the same pattern
as described in the compaction of the loose refuse
(see parts a, b, c, and d under Residential
Refuse-Loose). Most of the reduction in volume took
place at pressures below 1,000 psi. Above 1,000 and
up to 3,500 psi, the volume decreased continually but
at a lesser rate
The values obtained for the volume reduction
ratios of sacked household refuse were similar to
those of loose residential wastes. The computed
averages for the sacked refuse compacted at about
3,400 and 1,900 psi were about 13:1 and 11:1
respectively, as shown in Table 27.
The relationship between the loose densities and
the volume reduction ratio was the same as that
found for the loose refuse. That is, the reduction in
volume was always greater (17:1) when the density of
the uncompacted sacked refuse was lowest (4.8
Ibs/cuft).
The presence of sacks had no apparent effect on
the reduction in volume.
b) Bale Densities During Compaction
I lie densities ol sacked iciu.sc. during
compaction, were found to be of the same order of
magnitude as those of the loose residential wastes.
The computed values of the densities of 30 samples
of sacked refuse are given in Table 28..
As with loose residential wastes, the densities of
different sacked refuse samples were found to be
independent of the densities of the incoming refuse.
Furthermore, the average densities, and also the
maxima and minima, were close to those obtained for
loose refuse.
The values obtained by compaction of
precompacted sacked refuse from 3,500 to 6,000 psi
show that the high pressure did not increase the
density of the bales. Similar results were obtained
with other samples precompacted at 3,500 psi.
c) Volume Expansion and Bale Densities
After Compaction
As with all other types ot mixtures of household
wastes, the volume of the compacted sacked refuse
did not remain the same after removal of the
compaction pressure. The volume increase was again
found to be more rapid immediately after pressure
release. The increase in volumes and the associated
decrease in bale densities during an inital expansion
of 1 to 2 minutes are shown in Table 29.
The volume reduction ratio of the bales
compacted at about 3,500 psi decreased within 1 to 2
minutes after removal of pressure by about 31
percent of its original value. Simultaneously, the bale
density decreased from 94 to 64 pounds per cubic
foot. The average volume increase for bales
compacted at about 3,400 psi was 47 percent. The
average volume increase for bales compacted at about
2,000 psi was nearly 10 percent less. Nevertheless, the
volume of the bales compacted at lower pressures was
always larger after expansion than the volume of
bales compacted at the higher pressures.
d) Effect of Adhesives on Volume Reduction Ratios
and Bale Densities During and After Compaction
Several adhesive experiments weie earned out
with samples of 10 bags of paper-sacked refuse. In
each case the adhesive was sprayed on the outside of
the sacks immediately before compaction. The results
obtained with samples spraved with :i cellulose tvpe
of adhesive containing about 20 percent of solids
dissolved in water are given in Table 30.
As expected, the presence of adhesives had no
TABLE 29
Volume Reduction Ratios and Bale Densities of Paper Sacked
Residential Wastes During and after Compaction
Volume Reduction
Ratios (averages)
Dur ing
Compact ion
13 : 1
11:1
After 1 to 2 Mi n.
Volume Expansion
9 : 1
8 : 1
Average
Vol ume
1 ncrease
%
^7
38
Densities of Bales
(Ibs/cuft, averages)
Dur ing
Compact ion
9*»
85
After 1 to 2 Min.
Volume Expansion
64
63
Compact ion
Pressure
(psi)
3300 - 3500
1850 - 2000
58
-------
TABLE 30
Effect of Adhesives on Bale Densities and Volume Reduction
Ratios for Paper Sacked Household Refuse Compacted at
Different Pressure*-
No. of
Samples
5
3
Densi ties
of Loose
Refuse
(Ibs/cuft)
(averages)
6.5
6.6
Densities of Bales
(Ibs/cuft, averages)
Dur i ng
Compact ion
86
80
After
Spr ingback
1 to 2 Mi n.
66
5^
Volume Reduction Ratios
(averages)
Loose/
Compaction
Chamber
1J» : 1
12 : 1
Loose/
Spr ingback
1 to 2 Min.
10 : 1
8 : 1
Maximum
Compaction
Pressure
(psi)
3300 - 3500
1850 - 2000
effect on the compaction properties of the wastes
during compaction. The effect of the adhesive on
volume expansion during the first two minutes was
slight.
Initially, the volume of the compacted bales
increased nearly as rapidly as the volume of the
sacked refuse which was not sprayed. This was
probably due to the presence of an appreciable
amount of moisture in the diluted adhesive which
decreased the immediate effectiveness of the
adhesive. The expansion of bales compacted at about
3,400 psi was about 8 percent less- than the
expansion of the unsprayed bales. The main
difference between the sprayed and unsprayed bales,
however, was found to be in the appearance and
stability of the bales after standing. The sprayed bales
were less distorted and more rugged than those not
sprayed.
e) Effect of Pressure Holding Time, and Refuse
Properties on the Stability of Bales of Sacked Refuse
The stability and appearance of the paper-sacked
bales compacted in normal fast runs at about 2,000
and up to about 3,500 psi was very good. The
stability of bales compacted in fast runs at about
1,500 psi was acceptable. An improvement in
stability always resulted if the pressure to the bale
was applied for an extended time. Very stable bales
were produced by the addition of adhesives to the
outside of the paper sacks.
The stability and appearance of the compacted
plastic-sacked refuse was, as a rule, poor. The plastic
sacks tended to burst and adhered very poorly to
each other. Addition of adhesives to the outside of
the plastics appears to be essential for the compaction
of this type of sacked refuse.
The absence of excessive moisture (exclusion of
rain) proved to be a great asset in the compaction of
the paper-sacked refuse. It introduced very favorable
conditions with respect to the subsequent stability of
the compacted refuse. In addition, the paper sacks
remained largely intact during compaction. This
improved the appearance of the bales and also
prevented spillage of loosely adhering refuse
components from the outside of the bales.
It can be concluded, therefore, that paper-sacked
refuse, if compared to loose refuse, has distinct
advantages with respect to its compaction properties.
3. Shredded Residential Wastes
Only one truckload of shredded residential
wastes, received from Madison, Wisconsin, was
investigated in the present study.
The wastes (see Section Two) contained a high
proportion of paper products. The loose densities of
the individual samples varied only between 8.2 and
11.0 pounds per cubic foot. This is not surprising
since all refuse samples came from the same load. The
average moisture content, 10.7 percent by weight,
was low; it was comparable to that of dry household
refuse delivered either loose or sacked.
The relatively high densities of the incoming
shredded refuse, and its uniformity, were
undoubtedly the result of the processing which
reduced the void space and provided some mixing.
The loose refuse had the appearance of shradded
newspapers.
a) Volume Reduction During Compaction
I he volume i eduction ration ot the shredded
wastes compressed at different pressures are given
in Table 31. In addition, the table includes results
of the reduction in volume of two samples to which
water was added, and also the results of two samples
which were compacted for 5 minutes each at the
indicated pressure.
59
-------
The results show that the volume of the shredded
wastes decreased appreciably during compaction. The
average volume reduction ratio of the wastes
compacted at about 3,400 psi in fast runs was of the
order of 10 to 1. This result indicates clearly that,
although some reduction in void space was achieved
by shredding, a large amount of air was still trapped
in the refuse.
As with other types of wastes, a further
reduction in volume resulted when the pressure to the
bales was held for several minutes. The results
obtained with the samples to which water was added
show very clearly that moisture affects the
compaction properties of wastes. The volume of the
wet bales was larger than the volume of the dry bales,
and as a result the volume reduction ratio decreased.
The increase in bale size of the wet bales suggests
that the absorbed water caused swelling of the papers
in the shredded refuse, which as a result occupied a
larger volume than it would have in the absence of
excessive moisture. The swelling properties of papers
are most likely the cause of the partial
proportionality found between the volume reduction
ratio and the density of the incoming refuse (see parts
b and c, Residential Wastes-Loose).
b) Bale Densities During High Pressure Compaction
The average densities of the shredded samples
were, as a rule, several pounds higher than the average
densities of the sacked and loose wastes compacted at
the same pressure. This, however, does not necessarily
mean that the packing of the waste components in
the refuse bales was denser althoueh such an
interpretation is possible.
Calculations showed that weight losses due to
liquid extraction were similar for shredded and dry
loose residential wastes. In addition, loose residential
wastes, containing a similar low moisture content as
the shredded refuse, often produced bales of similar
densities.
The computed densities of the bales, during
compaction, are given in Table 32.
c) Volume Expansion of Bales and Bale Densities
After Compaction
The increases in volume and the associated
decreases in volume reduction ratios and densities oi
compacted shredded refuse are shown in Table 33.
The results show that the expansion in volume
was highest for.bales to which water was added. The
total moisture content of these bales was probably
close to 22 percent (a) and 28 percent (b) of the total
weight (see Section Two: Moisture in Shredded
Refuse). These wet samples lost up to about 7 pounds
in weight during compaction.
The wet re'luse bale:* expanded about 4U percent
in height and about 20 percent in length. Similar
results were also obtained with unshredded wet
household refuse.
The expansion of the non-wetted refuse
compacted at 3,400 psi was on the average about 31
percent in height, 4 percent in length and 3 percent
in width. Similar resulu were also obtained with the
paper-sacked and relatively dry loose refuse.
The increase in volume of the two bales
compacted for 5 minutes a* 1,850 and 3,400 psi was
TABLE 31
Volume Reduction Ratios of Different Sample of Shredded Refuse
No. of
Samples
2k
1
]
1
8
1
1
Average
Dens i t ies
of Loose
Refuse
(Ibs/cuft)
9. I*
8.3
10.2
10.9
10.2
9.9
9.9
Volume Reduction
Ratios During
Compact ion
(averages)
10.7 : 1
12.1 : 1
9-9 : 1
9.2 : 1
9.4 : 1
10.1 : 1
6.9 : 1
Compaction
Pressure
(psi)
3400
3400
3400
3^00
1850
1850
350
Comments
Normal fast runs
5 Min. pressure holding time
Water added: 1 ]% by wt .
Water added: 17% by wt.
Normal fast runs
5 Min. pressure holding time
Normal fast run
60
-------
TABLE 32
Densities of Bales of Shredded Refuse During Compaction
No. of
Samples
24
1
1
1
8
1
1
Average
Densities of
Loose Refuse
(Ibs/cuft)
9.4
8.3
10.2
10.9
10.2
9.9
9-9
Densities of Bales
(Ibs/cuft)
Maximum
103
-
-
-
100
-
-
Mi nimum
96
-
-
-
92
-
-
Average
101
99
98
98
95
98
66
Compact ion
Pressure
(psi)
3400
3400
3400
3400
1850
1850
350
Comments
Normal fast runs
5 Min. pressure
holding time
Water added:
11% by wt.
Water added:
M% by wt.
Normal fast runs
5 Min. pressure
holding time
Normal fast runs
TABLE 33
Volume Reduction Ratios and Bale Densities of Shredded Refuse
During and After Compaction
No. of
Samples
24
1
1 (a)
1 (b)
8
1
1
Volume Reduction Ratios
(averages)
Dur i ng
Compact ion
10.7 1
12. 1 1
9.9 1
9.2 1
9.4 1
10. 1 1
6.8 1
After
1 to 2 Min.
Volume
Expans ion
7.4 1
8.5 1
5.7 1
5-1 1
6.7 1
7.0 1
3.5 1
Volume
Expans ion
after
1 «- ~ O Min
°/
44
42
73
80
45
44
93
Densities of Bales
(Ibs/cuft, averages)
Dur i ng
Compact ion
101
99
98
98
95
98
66
After
1 to 2 Min.
Vol ume
Expans ion
68.6
69.7
56.0
55-0
67.3
68.0
34.0
Compaction
Pressure
(psi)
3400
3400 (51)
3400 (H20)
3400 (H20)
1850
1850 (51)
350
61
-------
about the same as that of the average expansion of
the bales compacted at the same pressures for a
fraction of the time.
The largest increase in volume, 93 percent
occurred after compaction of the refuse at about 350
psi. In this case the bale expanded primarily in the
length direction by about 40 percent, and about 26
and 9 percent respectively in the direction of height
and width. The bale produced was quite soft and
spongy and its stability was poor.
After the initial growth, the increase in volume of
the bales proceeded at a slower rate. A representative
example of the increase in bale volume during 24
hours is given in Table 34 for two shredded refuse
bales compacted in fast runs at 3,400 and 1,850 psi.
respectively.
Holding of pressure on the bale for 5 minutes
resulted in the formation of a very compact structure
which appeared to be more stable than those
subjected to the same pressure for a very short time.
However, additional information is needed to assess
the influence of holding time on volume expansion
after compaction of shredded refuse.
The appearance of the bales of low-moisture
content was superior to that of the bales of the same
moisture content produced by compacting loose
household refuse. It was also better than the
appearance of the paper-sacked refuse bales, which
was very good.
In conclusion, it should be pointed out that the
investigation was carried out with a single load of
shredded refuse of high paper and low moisture
TABLE 34
Volume Increase of Compacted Shredded Refuse With Time
Sample
1
2
Time
(minutes)
1
5
30
1440
1
5
30
1440
Vol ume
Increase
(*)
44
49
58
71
60
69
82
95
Compaction
Pressure
(psi)
3400
1850
The results given in Table 34 show that the total
increase in volume after 24 hours was about 71 and
95 per cent. It should be remembered, however, that
the values given represent the increase in volume of
bales which were allowed to expand freely in all
directions. As mentioned previously, the -degree of
volume expansion of bales confined into a given space
and piled on top of each other is likely to be less than
that found for bales allowed to grow unrestricted.
The densities of the shredded refuse bales, after
expansion, were approximately the same as other
refuse bales of high densities.
d) Effect of Pressure, Moisture Content, and
Pressure Holding Time on Bale Stability
_ The stability of the shredded reluse compacted at
1,850 and 3,400 psi was very good. The bales
produced from the dry refuse had straight sides and
sharp edges. The only bale which had poor stability
was the one which was produced at 350 psi. The wet
bales tended to bulge.
content, and that additional work is needed to
evaluate fully the effect of shredding on compaction.
4. Gas Development in Residental Waste Bales
To obtain information about the gaseous
decomposition products of compacted residential
waste bales, several gas samples were taken and
analyzed.
The bales were prepared from truck refuse
containing a large proportion of yard cleanings. The
composition of this refuse is given in Table 10.
Six bales were prepared in total. Each bale
contained 200 pounds of the refuse. However, two
samples were compacted after filling of «the refuse in
paper sacks, whereas the other four were made from
the loose refuse. In addition, three samples were
compacted at about 2,000 psi and three at about
3,500 psi.
Two bales containing loose residential wastes and
two bales containing paper-sacked residential wastes
were stored as they came out of the press. The
62
-------
TABLE 35
Gas Analysis and Bale Temperature of Compacted
Spring Cleaning Residential Wastes
Bales
Residential - Loose
(3500 psi)
Residential - Loose
(2000 psi)
Papersacked
(3500 psi)
Papersacked
(2000 psi)
Plastic covered
(3500 psi)
Plastic covered
(2000 psi)
Sampl i ng
(days)
4.5
8
4.5
8
4.5
8
4.5
8
4.5
8
4.5
8
% of Gas
C00
7.0
2.9
6.4
7.3
4.21
4.5
-
6.9
3.5
3.7
7.6
4.7
Oo
13.1
17-5
14.2
12.4
16.2
15.6
-
13.2
17.3
16.7
12.4
15.5
CO
0.009
trace
0.011
trace
0.013
trace
-
trace
0.019
trace
0.013
trace
CH,
none
none
none
none
none
none
-
none
none
none
none
none
Bale
Temperature (°F)
1 ns ide
105
102
129
105
118
100
115
115
106
106
97
92
Surface
95
93
125
H9
113
110
103
103
98
90
93
89
•v Time elapsed after bale was made.
(1) Mean value of both papersacked samples,
remaining two bales of loose residential wastes were
tightly wrapped in plastic sheeting and then stored.
The hut in which the bales were stored was kpr>t
at a temperature of about 85 ± 5 F.
Alter J day oi storage, the two samples wrapped
in plastic were found to be warm to the touch. In
addition, droplets of water had started to develop on
the inside of the plastic cover. The samples not
wrapped in plastic remained cool and dry to the
touch.
After 3 days of storage, all samples were covered
in plastic to allow accumulation of the gaseous
products. Within 24 hours those nof wrapped
previously also released a large amount of moisture
and were warm to the touch.
On the fourth day of storage gas samples were
taken from each bale by insertion of a rubber tubing
inside the cover. Subsequently, a second set of gas
samples was taken from the bales which, after 8 days
of storage, were still in their plastic cover.
The analysis of the gases was made by the
Peoples Gas, Light and Coke Company, Chicago,
Illinois. The results of the ga» analyses and
measurements of the bale temperature taken at the
time of gas sampling are given in Table 35.
The results of the gas analysis (Beckman,
Chromotography, and Infrared) show that the
collected gases did not contain methane (CH4) and
that the main decomposition product was carbon
dioxide (CO2). This, together with the observation of
the large amount of water formed on the inside of the
plastic wrapping of all bales, indicates strongly that
the bacterial activity was aerobic.
The temperature of the bales, taken at the time
of gas sampling, was found to be the highest for the
bale of loose residential wastes compacted at 2,000
psi and wrapped in plastic 24 hours before sampling.
On the other hand',i he temperature was lowest for the
bale compacted at the same pressure and containing
the same loose refuse, which was, howevei, wrapped
in plastic immediately after compaction.
The results of the gas analysis and temperature
seem to indicate that the decomposition of organics
was more vigorous in bales compacted at 2,000 psi
than in the other bales. This might have been due to
the fact that these bales contained more air and that
its diffusion through the bale was facilitated by the
looser compaction.
461-084 O - 72 - 6
63
-------
III. COMPACTION OF SYNTHETIC REFUSE
SAMPLES
Several series of experiments were carried out
with samples which were specially prepared for
testing purposes. The composition and the properties
of the uncompacted synthetic samples used in the
investigation are described in Section Two.
The procedure adopted for compaction was the
same as that used in the compaction of the residential
wastes delivered from households. The samples were
subjected to compaction in the same press (Fig. 3)
and the applied pressure and the change in volume
was measured electronically as described before (see
Section I).
The results of this part of the experimental
study, which was designed to investigate in more
detail the compaction properties of residential wastes
and other refuse components of interest, are given in
the following sections.
1. Synthetic Refuse Mixtures-Loose
Two types of refuse mixtures were prepared,
both representing dry city household refuse of high
paper content.
Each mixture contained about 60 weight percent
of mixed paper products and 40 weight percent of
other components which included metals, glass and
ceramics, food wastes, liquids, construction wastes,
plastics, textiles, rubber, leather, and dirt. The types
and respective percentages of the individual paper
products and other components are given in Table 15.
The moisture content of mixtures 1 and 2 was
estimated to be about 19 and 14 weight per cent,
respectively (see Section Two, Moisture Content of
Synthetic Waste Mixtures).
Several samples of the same composition were
used to investigate the effect of compaction variables
on bale formation and bale properties. Eighteen
samples of synthetic loose refuse were subjected to
compaction. Six samples contained Mixture 1 and 12
samples contained Mixture 2.
a) Effect of Pressure on Bale Volume During
Compaction
As with other refuse samples, the refuse was first
gathered by the first and second ram into a space of
about 7.8 cubic feet. The refuse was then compacted
by the third high compression ram. During the final
operation the decrease in volume was accomplished
by the reduction of the height of the bale: the other
two dimensions remained unchanged. The decrease in
bale height of six 200-pound samples (three samples
of each mixture) compacted at about 1,500, 2,000
and 3,500 psi respectively, is shown in Figure 14.
It can be seen that the reduction in volume of all
samples started at about 150 psi. The decrease in
volume up to about 300 psi was nearly the same for
samples of both mixtures. However, above 300 psi
the volume of the samples made up from Mixture 1
was usually lower than the volume of the samples
made up from Mixture 2.
The difference in volume reduction between the
samples of the two different mixtures was slight.
However, the results reflect the sensitivity of
compaction to composition. Mixture 1, which
contained more moisture, compacted to a higher
degree than the drier, but otherwise similar, Mixture
2.
Compaction at about 3,500 psi reduced the
original volume (7.8 cuft) by about 69 per cent (a)
and 67 per cent (b).
Mixture 2 were about 7.6 and 8.0 pounds per
cubic foot, respectively. However, the computed
volume reduction ratios of the two types of samples
were similar to those obtained with residential wastes
of higher loose densities.
The average volume reduction ratios of different
samples compacted at different pressures are given in
Table 36.
b) Effect of Pressure Holding Time on Bale
Volume During Compaction
The effect produced by applying pressure to the
bale (Mixture 2) for a length of time is shown in
Figure 15.
The decrease in bale height at about 850 to 1,000
and 1,500 psi was, after holding of pressure, nearly
equivalent to the decrease which was achieved by
compaction in normal fast runs (full curve) at a 700
psi highar pressure. At about 2000 to 2500 psi the
decrease with time was nearly equivalent to that
obtained in a fast run at about 500 psi higher
pressure. Increase in pressure holding time from 5 to
10 minutes had no effect.
The examination of the various recordings taken
during the above runs, and for other refuse samples to
which pressure was applied for a period of time,
showed that the decrease in volume shown in Figure
15 was achieved in less than one minute.
c) Volume Expansion of Bales After Compaction
The increase in volume of the compacted bales of
both mixtures was followed after removal from the
press over a period of 24 hours. Measurements were
taken after 1,5, and 30 minutes and then after 24
hours. The increase in volume within the first minute
was found to be usually more than 50 percent of the
increase after 24 hours
64
-------
42
o
c
en
ro
co
12 -
a = Synthetic Mixture 1 (200 Ibs)
b * Synthetic Mixture 2 (200 Ibs)
0=0- 3500
X = 0 - 2000
• =0-1500
2500
Ram Pressure
FIGURE 14
Synthetic Refuse—Loose. Decrease in Bale Height
as a Function of Pressure.
3500
i n ps i
TABLE 36
Average Volume Reduction Ratios of
Synthetic Refuse Mixture1;
Volume Reduction Ratios
(averages)
Mixture 1
10.0 : 1
9.0 : }
8.8 : 1
8.1 : 1
Mixture 2
9.0 : 1
7.8 : 1
7-5 : 1
6.9 : 1
Compaction
Pressure
(psi)
3500
2000
1500
1000
65
-------
The increase in volume was found t« be related
to the compaction conditions. Bales compacted at
higher pressures expanded less than those compacted
at lower pressures. The volume increase of bales
compacted at the same pressure was found to be
lower if the compaction pressure on the bales was
held for several minutes.
The average percentage increase in volume of
200-pound bales of both mixtures, compacted in fast
runs at 1,500, 2,000 and 3,500 psi (full lines), and
the increase of bales compacted 5 to 10 minutes at
about 1,000, 1,500 and 2,000 psi (dashed lines), is
shown in Figure 16.
The increase in bale volume was found to be least
for a bale compacted for 25 minutes at successively
higher pressures from 1,000 to 3,000 psi (see Fig. 15,
dotted line) and then finally at 3,500 psi.
The average values obtained for the bales
compacted at 2,000 and 1,500 psi for 5 to 10
minutes were close to tnose of the bales at 3,500 psi.
Bales compacted at 1,000 psi for 5 and 10 minutes
expanded less than those compacted in fast runs at
1,500 (Fig. 16,).
The increase in pressure holding time from 5 to
10 minutes had no apparent effect.
The computed volume of nine bales compacted
for 5 to 10 minutes at different pressures (Mixture 2)
and the volume of the expanded bales after 1 minute
and 24 hours is shown in Figure 17. The volume of
three bales compacted in fast runs, after 24 hours
expansion, is given for comparison (dashed line).
The stability of the synthetic refuse bales
compacted in normal fast runs was comparable to the
stability of high-paper-content dry residential wastes
compacted at the same pressures. Bales compacted at
about 2,000 psi and higher pressures were stable.
Reasonably stable structures were also obtained after
compaction at about 1,500 psi: however, these bales
-------
tended to bulge. A distinct improvement in shape and
compactness resulted in each case in which the bales
were compacted for several minutes.
Recordings of changes in bale height with time of
pressure application indicated that a maximum
reduction in volume was reached after holding of
pressure for less than 30 seconds. Since an equivalent
decrease in volume was reached only at higher
pressures in fast runs, and since an increase in
pressure always improved the stability of the bales, it
is likely that less than 1 minute of pressure holding
time will be required to achieve the effect produced
by the increase in pressure.
A comparison of the final volume (after 24
hours) of bales compacted with time and of bales
compacted in fast runs at low pressures shows that an
improved stability equivalent to an increase of about
750 psi in pressure was achieved by holding the
pressure for 5 minutes. It is, therefore, reasonable to
expect that bales compacted at about 1,000 psi for 1
minute should be as stable as those compacted at
1,500 psi in fast runs. Similarly, bales compacted for
1 minute at 1,500 and 2,000 psi should be as stable* as
those compacted at 2,000 and 2,500 psi in fast runs.
2. Synthetic Mixtures in Paper Sacks
A series of experiments was also made with
samples of synthetic Mixtures 1 and 2, which were
placed into paper sacks and then compacted. This was
done since it had been found that compaction of
paper-sacked refuse offered advantages over that of
loose refuse. These advantages were associated with
the elimination of rain from the refuse and also with
the reduction in spillage of loosely adhering refuse
components from the compacted bales (see
Residential Wastes in Paper Sacks).
Each compaction experiment was carried out
with nine bags filled with synthetic refuse. The
compaction properties of the two sacked mixtures are
on the following page.
2V
30'
• =
o =
X =
A =
1000-3000 (25')-3500
2000 (5' & 10') /
1500 (51 & 10') /
1000 (51 & 10') */
< —
20
30
*40 50 60%
Volume Increase in Percent
FIGURE 16
Synthetic Refuse Loose. Average Volume Increase of
Bales of Both Mixtures Compacted With and Without
Holding Pressure.
67
-------
a) Effect of Pressure and Pressure HoldinjfTime on
Bale Volume During Compaction
The compaction of the paper-sacked refuse
of Mixtures 1 and 2 followed the same pattern
as that of the loose synthetic mixtures. As be-
fore, the volume of the bales containing Mixture
2 was slightly larger than that containing Mixture 1.
However, the volume of the compacted sacked refuse
seemed to be slightly larger than that of the loose
refuse.
The decrease in bale height of 20 samples of 200
pounds each (Mixture 2), compacted by holding of
pressure and in normal fast runs is shown in Figure
18. The dotted line represents the result of one run
during which the pressure was held successively for 5
minutes at about 1,000, 1,500, 2,000, 2,500, and
3,000 psi.
The results obtained with the paper-sacked
samples followed the same pattern as found with the
loose wastes. The decrease in volume recorded for the
samples compacted for 5 to 10 minutes was also
reached after less than 1 minute of holding time.
b) Volume Expansion and Bale Stability of
Paper-sacked Synthetic Refuse
The increase in volume of the compacted bales of
paper-sacked refuse after release of pressure appeared
to be higher by several percent than the volume
increase of the baled loose synthetic refuse. However,
since variations in volume expansion of individual
bales of both loose and sacked refuse were found,
additional work would be necessary to determine
whether the observed effect is reproducible.
As with loose refuse, the average volume
expansion was found to be less for bales compacted
0)
0)
u_
o 4
-Q
O
c
\ Mixture 2 (200 Ib samples)
V
\
V
Volume During Compaction (5 to 10 min. holding time)
1000
1500 2000 2500 3000
Ram Pressure in psi
FIGURE 17
Synthetic Refuse-Loose. Volume Changes of Bales
Compacted for 5 to 10 Minutes.
3500
68
-------
22
_
u
c
en
0)
I
a)
CO
12
O = zero holding time
y = 5 to 10 minutes holding time
= one run
500 1500 2500
FIGURE 18 Ram Pressure
Paper-sacked Synthetic Refuse—Decrease in Bale
Height During Compaction With and Without
Holding of Pressure.
3500
in ps i
at a given pressure for several minutes. The average
expansion for bales compacted at about 1,000 and
1,500 psi in fast runs and after holding of pressure for
5 and 10 minutes is given in Table 37.
The increase in bale volume of the paper-sacked
synthetic refuse compacted at low pressures for
several minutes was about 15 to 20 per cent less than
for bales compacted in fast runs. At higher pressures,
the decrease in expansion was about 6 volume per
cent.
As with all refuse bales, the expansion was
highest in the height direction. However, the length
of the bales (second highest expansion direction)
increased slightly more than the length of the bales of
the loose refuse compacted at the same pressure.
The stability of the paper-sacked refuse bales was
either better, or comparable to, the stability of the
loose refuse bales compacted under the same
conditions. The sacked bales had the appearance of a
packaged bundle.
3. Synthetic Paper-Water Samples:
Moisture Experiments
It was found that a small amount of moisture has
a beneficial effect on the compaction of residential
wastes of high paper content. In small quantities it
facilitates the bending and breaking of the cellulose
fibers and fosters adhesion between the papers. In
very large quantities, however, it leads to the
formation of paper pulps which hinder compaction.
Difficulties with respect to compaction were
TABLE 37
Volume Increase of Paper-sacked Synthetic Refuse Bales
After Compaction at Low Pressures
Compact ion
Pressure
(psi)
1000
850-1000
1500
1500-1600
Time
(min.)
(5'&10'.)
(5'&10')
Average Volume Increase (%}
\ Minute
52%
3*»
48
30
5 Minutes
55£
41
55
36
30 Minutes
7^1
51
66
k]
2k Hours
781
57
71
5**
69
-------
experienced with waterlogged residential wastes
exposed to rain. They resulted mainly from the
formation of paper pulps which tended to be released
with great force from the press openings during high
pressure compaction.
In view of the large quantities of papers usually
found in wastes, it was felt that additional
information on the interaction of moisture and
papers was needed to determine the quantity of water
which can be accepted without impairing the
compaction of residential wastes.
a) Effect of Moisture on Bale Volume During
Compaction
Several series of experiments were maik with
samples containing: (1) paper mixtures which were
predried; (2) paper mixtures which were not predried;
(3) newspaper sheets not dried but separated; and (4)
newspaper bundles not dried. A premeasured amount
of water was added to each paper sample. The
paper-water mix was then left to stand at least
overnight. (For details see Section Two: Synthetic
Samples of Paper and Water.)
In order to compare the effect of different
moisture contents on the compaction properties of
different samples, all measured values obtained with
different weight samples were computed to a
standard weight per sample of 200 pounds. This
weight represents the total weight of water and paper
in each sample. The weight percentage of moisture in
each sample was then determined and its effect was
evaluated.
It was found that the height of the compacted
bales, during compaction, decreased as the weight
percentage of moisture was increased. In other words;
the replacement of papers by moisture did result in
the t'ormation of smaller bales than were obtained
with samples of the same weight which had more
solids and less water. The decrease in bale height of
200-pound samples as a function of moisture content
is shown in Figure 19. Calculations show that 100
o
c
O)
_OJ
0)
CO
12
O
D
A
•
partially dried paper mix
not dr i ed mix
newspaper sheets
newspaper bundles
10
20
30
50
Wt. % Moisture
HCURt 19
Effecfof Moisture Content on Bale Height During
Compaction of Paper Samples Compacted at About 3500 psi.
70
-------
pounds of water occupies less than 50 per cent of the
volume occupied by 100 pounds of paper mixtures,
and slightly more than 50 per cent of the volume
taken up by newspapers.
The increase in density resulting from the
decrease in volume of samples of equal weight was
found to be about 5.0 pounds per cubic foot for an
increase of about 10 weight per cent of moisture (see
Figure 20).
b) Volume Expansion After Compaction
As a Function of Moisture Content
The increase in volume of the compacted paper
samples, after release from the press, was found to be
related to the moisture content. Samples containing a
larger proportion of moisture expanded more in a
given time period than those containing less moisture.
A 10 percent increase in moisture of samples
containing 10 to 35 weight percent of moisture
usually resulted in an increase in volume of about 1C
percent. Above 35 weight percent, the increase in
volume was larger. Bales containing more than 40
weight percent of added water tended to disintegrate
immediately after release of pressure.
The expansion of mixed paper samples, over a
period of 24 hours, containing 10 to 50 weight
percent of water in addition to absorbed moisture is
shown in Figure 21.
c) Stability of Different Paper-Water Samples
The stability of all paper bales which contained a
very large amount of moisture was found to be poor.
However, an appreciable amount of moisture was
accepted by the papers without developing pulps.
Most paper samples composed of 50 per cent paper
and 50 per cent water were found to be unstable. In
some cases, paper samples of much lower moisture
c'ontent developed cleavages and slowly disintegrated.
Wetted newspaper bundles folded during
compaction tended to unfold, even after an addition
of about 45 percent of water. The folded paper
bundles were, in this case, not sufficiently wet to
allow breakage of fibers in the bends. As a result,
most compacted bales of paper bundles were
unstable, irrespective of the moisture content.
Separated newspapers and paper mixtures, to
which up to about 35 weight percent of water was
added, were reasonably stable. The actual moisture
content of these and all other bales was probably
about 10 percent higher since the papers contained
absorbed moisture before the addition of water.
Expansion of the paper-water bales became more
100 -
= 90
o
80
-------
three dimensional with increase in moisture content.
For example, the bale containing 50 percent of water
expanded after 10 minutes by about 28 percent in
height and by about 26 percent in length.
Recompaction of bales which had fallen apart did
not produce stable units.
4. Synthetic Samples of Papers and Adhesives
A limited series of experiments was carried out
with paper mixtures to text the effect of adhesives on
the volume expansion and stability of paper bales.
The adhesives used are described in Section Two of
this report. The effect of these adhesives on the
compaction of paper-sacked refuse was discussed in
the section on residential wastes.
Each paper sample was first wetted in order to
raise its moisture content to about 20 weight percent.
The adhesives were dissolved in water and then
introduced into the mix by spraying. The paper
refuse was subsequently compacted at about 3,500
psi. Four different water-soluble adhesives containing
15 percent solids were used. Both the compaction
volume and the expansion volume of the different
samples were found to be similar irrespective of the
adhesives introduced.
The average volume increase was about:
42 percent after 1 minute,
47 percent after 5 minutes,
54 percent after 30 minutes, and
62 percent after 24 hours.
The over-all increase in volume with time was
about 15 volume percent less than the volume
increase of similar samples which did not contain
adhesives. It is likely that a further reduction in
volume expansion would have been achieved with
adhesives containing less water or with initially drier
refuse samples. Application of heat during
compaction is also likely to be beneficial since it
could reduce the moisture level and thereby improve
the effectiveness of the adhesives.
Although the volume expansion after compaction
was not substantially reduced by the addition of the
adhesives, the paper bale stability was distinctly
improved and the appearance of the bales was
excellent. The work with adhesives was not pursued
further because the stability of the baled household
refuse was found to be quite good without the use of
adhesives.
1*0
50
100 110 120
Volume Expansion %
130
FIGURE 21
Volume Expansion of Compacted Paper Bales Containing
10 to 50 Weight Percent of Added Water
72
-------
5. Compaction Properties of Selected Refuse
Components
The compaction properties of individual refuse
components of interest were tested, either alone o r
in combinations.
The properties of different refuse components
compacted at about 3,500 psi are described below:
1. Rubber Tires. Several samples of rubber tires
were subjected to compaction. However, they
could not be compacted. After release of
pressure the tires always separated.
2. Rubber Tires Enclosed in Wire Mesh. The
compacted bundles of tires enclosed in the
wire mesh always expanded rapidly. The wire
mesh, depending on its strength, usually burst
open at a few or many welded spots.
3. Shredded Rubber and Residential Wastes.
Residential waste, containing about 25 per-
cent of small rubber pieces, produced good
bales. Shredded rubber on its own could not
be compacted.
4. Metal Cans and Oversized Metalic Wastes.
All metallic waste products, including
refrigerators, washing machines, stoves, and
appliances, produced excellent bales.
5. Oversized Wastes. Mixtures of refrigerators
or other oversized metallic wastes, together
with furniture and textiles produced very
stable bales.
6. Oversized Wastes and Household Refuse.
These mixtures produced very good bales.
7. Plastic Scrap. Compacted mixtures of
plastics did not hold together after release of
pressure.
•°. Very Dry Papers. Such papers did not
produce stable bales.
9. Vegetables, Fruits, Meat Scraps. These
wastes could not be compacted on their own
or in combination.
10. Vegetables, Fruits and Residential Refuse.
An appreciable amount of food pulp was
formed by compacting residential wastes
which contained a large amount of fresh
vegetables or fruits. Addition of about 25
weight percent of vegetables to residential
wastes produced a large amount of fine pulp
which was partially released from press
openings already at about 900 psi. The pulp
which adhered to the outside of the
compacted bale fell off after removal of
pressure.
11. Cooked Meats and Residential Refuse.
Similar results as those obtained with
vegetables and fruits were obtained with meats
containing a large amount of moisture.
12. Vegetables and Wood Shavings. The addition
of vegetables to wood shavings produced
unstable bales.
13. Wood Shavings. Wood shavings, alone,
produced relatively good bales.
14. Wood Chips and Residential Refuse.
Mixtures of residential wastes and wood chips
produced good bales.
6. Measurements of Load Distribution During
Compaction of Synthetic Mixtures and Other
Refuse Samples
Two types of load distribution measurements
were carried out using penetration gage assemblies.
Initially, one penetration gage assembly was
introduced into the compaction chamber adjacent to
the third ram to measure load distributions at the
interface between the high pressure ram and the
refuse bale. Subsequently, two penetration gage
assemblies were used, one next to ram three and the
other adjacent to the coverplate directly opposite ram
three. The latter arrangement was used to measure
load losses across the bale during compaction.
The basic principle of the measuring method and
the gage assemblies themselves were described
previously (see Section One, 11-3). In brief, the gage
contained 252 steel balls for peak force
measurements. The diameters of the indentations in
the measuring plate were calibrated for different
applied loads. The calibration curve obtained was
then used to determine the peak load of each
indentation.
Contour drawings ( not shown) were made of the
load levels of the indentations produced during
compaction in the bottom and top plates. The long
side of the plates was marked from A to R. This side,
which coincides with the 20-inch length of the bale,
was parallel to the first ram of the press. The plate
side perpendicular to the first ram (parallel to the
second ram) of 16 inches width was marked from 1
to 14.
The loads of the individual indentations were
summed along lines parallel and perpendicular to the
face of ram one. The resultant total load of each row
was then plotted to indicate the load distribution
across the place parallel to the first or second ram, in
each case starting at the corner position of these two
rams. The total load distribution at the bottom and
top of the bales is shown for different samples and
different compaction conditions in Figure 22.
The load distribution at the bottom of the bales
(adjacent to ram three) is given in Figure 22, 1 and 2,
for samples containing Residential Wastes (A); Tin
Cans (B); and Shredded Residential Wastes (C). These
73
-------
e
*•* €
o 5
l— o
32
I
(0001
(0001 x sq[) peon
oo „,
L-
M> §
(0
, 8
4-1 V
— O
a,
o
H
13
(0001 x sq|) peoi
(0001 x sqi) peon
81
3
Q
T3
O
O
(0001
(0001
74
-------
samples were compacted at about 3,400 psi hydraulic
pressure.
The load distributions at the bottom and top of
bales are shown for a synthetic sample of sawdust
(Fig. 22, 3 and 4) and for two synthetic refuse
mixtures in paper sacks (Fig. 22, 5 and 6). The
compaction pressure used in the compaction of
sawdust was about 3,400 psi and for the two synthetic
mixture samples was about 1,000 psi (a) and 1,500
psi(b).
The results presented in Figure 22 show several
distinct features. In most cases, the load distribution
pattern was found to be more uniformly parallel to
ram one than parallel to ram two. It seems, therefore,
that the sweeping action of the first gathering ram
and the second ram tend to introduce areas of varying
densities perpendicular to the first ram face. Low
load values were recorded primarily adjacent to the
sides parallel to the first and second ram face (row A
and row 1). However, a sharp decrease in load values
is also found next to the other two sides of the
compaction chamber (row R and row 14).
A comparison ot the load distribution patterns of
the different waste samples show that sawdust
produced the most uniform loading pattern of the
materials tested. This is not surprising since its
consistency resembled more that of a granular
homogeneous substance than any of the other
materials tested. The load values obtained for rows
next to the first and second ram were found to be
higher at the bottom than at the top of the bale. The
decrease of the total load value of row A and row 1 at
the top of the bale indicates that load losses had
occurred during the high pressure compaction.
With respect to the other samples, the most
uniform load distribution was always found parallel
to the first ram face (see lower figures). They were
also usually more uniform at the bottom face of the-
bales than at the top face. Pronounced load peaks
were recorded for load patterns parallel to ram two
(see upper figures).
The loads next to the bottom face (Fig. 22, 1 and
2) were more evenly distributed for shredded wastes
(1C and 2C) than for the residential waste (1A and
2A), and for Tin Cans (IB and 2B).
Bell-shaped curves were obtained both with
residential wastes and with the simulated synthetic
mixtures of residential wastes (Fig. 22, 2 and 6). It
can be seen that the load distribution curves parallel
to ram two show pronounced single peak maxima at
the center of the bale face (synthetic mixture) or
slightly off the center (residential wastes). The
developed peak force is found to be especially
pronounced at the top of the bale compacted at
1,500 psi (Top b, Fig. 22,6).
The total load transmitted to the top plate was,
as a rule, less than the load experienced by the
bottom plate. The load losses occurred as a result of
shearing effects by which part of the applied force
was lost to the side walls of the chamber (see first and
last rows in Fig. 22, 3, 4, 5, and 6).
Calculations show that the over-all load loss for
sawdust compacted at 2,400 psi was only about 7
percent. Higher losses were found to occur at low
pressures, and with less uniform materials. The
over-all loss for the paper-sacked bales, compacted at
1,500 and 1,000 psi, was about 23 percent and 27
percent, respectively.
The presented results show that peak loads can
be developed both at the bottom bale face, resting on
the high pressure ram, and at the top of the bale. At
present it is not clear whether the peaking occurs
primarily as a result ot individual material properties
of the bale components, or whether it is related to
the compaction conditions. Further work in this
direction could provide information which could be
of great value in the design of compaction presses.
75
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(1)
(2)
(3)
(4)
Compaction of Solid Wastes:
(1) Compaction Press;
(2) Loading of Press Charging Box,
(3) Weighing of Compacted Bale;
(4) Electronic Measuring Equipment.
76
-------
(5)
(6)
(7)
(8)
Compaction of Loose and Paper-Sacked Residential Wastes:
(5), (6) Wastes in Charging Box
(7) Compacted Bales of Loose Wastes Containing Shredded Tires
(8) Ejection of Paper-Sacked Bale after Compaction
77
-------
(10)
(11)
(12)
Individual Bales Compacted at about 3,500 psi;
a) Spring Cleaning Refuse of High Dirt Content: (9) Loose; (10) Paper-Sacked
b) Winter Refuse of High Paper Content: (11) Loose; (12) Paper-Sacked
78
-------
(14)
(15)
(16)
Compacted Winter Refuse — Loose and Paper-Sacked
(13) Left Set 2,000 psi, Right Set 3,500 psi, Strapped to Pallets for Truck Transport
(14) Spring Refuse Containing Wood Chips
(15) and (16) High Dirt Content Spring Cleaning Refuse
461-084 O - 72 - 7
79
-------
(17)
(18)
(19)
(20)
Bales Compacted at about 2,000 psi:
(17) Paper-Sacked Spring Refuse
(18) Paper-Sacked (left) and Loose (right) Winter Refuse, Strapped to Pallet for Truck Transport
(19) Spring Cleaning Refuse Loose
(20) Spring Cleaning Refuse Paper-Sacked
80
-------
' i
(21)
(22)
•M',
(23)
(24)
(21) and (22) Paper-Sacked Refuse, Large Bales, Compacted at about 3,500 psi
(23) Temperature Measurement of Plastic Covered Bales Used for Gas Analysis
(24) Appearance of Refuse Bale after 5 Days of Decomposition Inside Plastic Cover
81
-------
(25)
(26)
(27)
(28)
(25) High Dirt Content Refuse Compacted at about 2,000 psi for 5 Minutes
(26) Spring Cleaning Refuse Compacted at about 1,000 psi for 10 Minutes (front) and High Paper Content
Synthetic Refuse Compacted at 1,000 psi (back)
(27) Synthetic Refuse Compacted at about 750 (left) and 1,000 psi (right) for 5 Minutes
(28) Shredded Refuse Compacted at about 2,000 psi
82
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(29)
(30)
(31)
(32)
(29) Paper-Sacked Refuse Compacted at about 750 psi for 5 Minutes
(30) 1,000 psi for 5 Minutes
(31) 1,000 and 1,500 psi for 5 Minutes
(32) 2,000 psi for 5 Minutes
83
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(33)
(34)
(35)
(36)
(33) Oversized Waste Bale
(34) Paper Mixture Bales Containing 45% (left) and 35% (right) of Water
(35) Large Bale Containing Dry Leaves, Clippings and Dirt
(36) Compacted Bale of Bedsprings (top). Refuse Mixtures with Ultra-High Metal and Can Content (bottom)
84
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(37)
(38)
(40)
Compacted Bales after Handling and Relatively Long Term Exposure to Weather Conditions.
(37) Paper-Sacked Residential Wastes
(38) Spring Cleaning Residential Wastes — Loose
(39) Shredded Wastes
(40) Paper Mixture Bales of High Initial Water Content
85
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CHAPTER IV
THE STABILITY OF SOLID WASTE BALES
IN TERMS OF RAIL-HAUL SYSTEMS
This chapter of the report deals with one of the
key aspects of the total project: the stability of the
compacted solid waste bales. As indicated in Chapter
II the requirements for any given bale form and size
mandate that the bale bear a relatively stable
configuration until it is disposed of in a sanitary
landfill.
SECTION ONE-BASIC STABILITY
FACTORS AND CONCEPTS
In general, stability is defined as the tendency to
remain in a given state or condition without
spontaneous change. This implies the capability of
possessing or developing forces equal to or greater
than any disturbing forces capable of causing
instability.
The term and concept of stability is applied in
many ways in different fields. Even with respect to
solid waste bales, stability might be considered
primarily or exclusively in terms of, for example,
chemical stability, thermal stability, and mechanical
stability including specifically the aspects of
dimensional stability and structural stability.
Within the context of this section of the report,
the term stability is used to denote the mechanical
stability of compacted solid waste bales. In particular,
the term is used to denote the resistance of the
compacted bales against their structural disintegration
by the application of mechanical forces.
It is, of course, recognized that chemical
instability induced by biological activity may
ultimately be the major cause for any mechanical
and/or structural instability of the bale. However, to
become effective in this respect both the biological or
chemical degradation forces appear to require a
longer period of time than the "shelf life" needed for
solid waste bales in rail-haul operations.
Concerning the bale itself, the mechanical
stability has to be viewed with respect to the
characteristics of a highly heterogeneous composite
solid. As indicated throughout this report a solid
waste bale, as a rule, represents neither a single solid
nor a solid of uniform or even relatively uniform
material composition and/or material distribution.
Since the individual components of most solid waste
bales exhibit both elastic and inelastic properties, the
over-all characteristics of the bales might be
considered akin to those of semi-elastic solids.
This finding is highly significant within the
context of the current investigation. The structural
stability of solid waste bales is determined primarily
by the strength of the adhesive or the interlocking
bonds formed between the solid waste components
by the application of pressure during compaction.
Consequently these bonds may be loosened by either
(a) the internal elastic forces or resiliency inherent in
the material composition or (b) the application of
external forces from the outside or (c) a combination
of both force activities.
The expansion or springback forces developed
within the bale are treated separately in Chapter
III of this report. The major part of their activity
occurs immediately and within a relatively short
period of time after release of the compaction
pressure. These forces and the counteracting cohesive
forces determine primarily at that time, the volume,
shape, and the inner structrual stability of the bale.
As a result, bales which remain intact after exit
from the press may, for practical purposes, be
considered as being in equilibrium with respect to the
interaction of their internal cohesive and expansive
forces. But stability in terms of just the bale, i.e.,
cohesiveness of the unit and retention of
configuration, is not enough for rail-haul. Concerning
both rail transport and the material handling
involved, the stability of bales must also be
established with regard to forces applied from the
outside through impact, vibration, pressure, and load.
SECTION TWO-STABILITY
TEST CONSIDERATIONS
To ascertain the stability of compacted bales
with respect to solid-waste rail-haul, it is necessary to
consider the operating requirements of both the
individual system elements and the total system itself.
In particular, it is necessary to ascertain: bale stability
in terms of rail transport, bale handling at the transfer
station as well as the disposal site, and bale storage
conditions and time.
I. BALE STABILITY DM TERMS
OF RAIL TRANSPORT
Within the solid-waste rail-haul environment the
shipped goods are subject primarily to longitudinal
and/or lateral and/or vertical shock and vibration
forces. The total amount of these force applications
is, of course, influenced by factors such as travel
distance and travel time.
1. Longitudinal Shock and Vibration
Longitudinal vibration does not exist at
amplitudes sufficient to cause damage to the lading.
87
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This vibration is caused when the springs of one
wheel truck move vertically 180 degrees out of phase
with respect to the springs of the other truck. This
vibration often is referred to as pitching or rotational
vibration.
All longitudinal shocks involve an impact
between two rail cars and generally the cars are either
traveling in the same direction or one is standing. In
moving trains a certain amount of movement must be
allowed between the car-end connections. This, in
turn, allows for some slack in car movements within a
train. During travel this slack is stretched or taken up
because of variations in track gradient, curves,
braking, or acceleration. Due to the total car weights
and traveling speeds involved, these slack movements
result in longitudinal shocks in either, or both,
directions. However, even a severe run-in during such
movements is generally equivalent to only a
5-mile-per-hour impact.
Experience has shown that most commodities are
not damaged by impacts at speeds of 5 or less miles
per hour. But damage does occur during shipment
and the railroad yard operations have been found to
be the source of most impact damages. This holds
true regardless of whether the cars are flat switched
or sorted by modern gravity systems.
The typical performance of a railroad
classification yard with respect to the generation of
impacts of varying severity is given in Table 38. The
data were established by the Technical Research
Department of the Penn Central Railroad and by
Pullman Standard, a Division of Pullman
Incorporated. The Pullman Standard figures are based
on 1,568 car impacts, measured over a period of 3
months in 1950. The Penn Central figures are based
on systemwide averages of 10,000 measurements per
year over a 2 year period.
The data in Table 38 indicate that, contrary to
popular belief, only about 15 percent of all yard
impacts exceed impact speeds of 6 miles per hour.
The average impact appears to occur at a speed of 5
miles per hour or less. In terms of railroad operations,
impact speeds of 6 or more miles per hour are
considered "rough handling" while impact speeds
between 5 and 6 miles per hour are considered
borderline cases. In most cases, the forces of a
longitudinal shock exist for about 0.1 second.
However, a loaded rail car might be handled
several times in a manner akin to classification yard
operations. In a rail-haul system this might occur
during switching at the transfer station or at the
disposal site and during the assembling of a train
enroute, e.g., the adding of cars from communities
included in the makeup of a single tram.
The probability of impact occurrence in
sequential switching operations has also been
established by the Penn Central Technical Research
Center. Data on 20.000 measurements are given in
Table 39 on the following page.
The data indicate, for example, that the
probability of a car being struck by an impact of over
6 miles per hour while passing through three
switching yards is about 1 in 3. In five switching
yards, an impact at a speed of more than 6 but less
than 7 miles per hour might happen to every other
car.
From these data it can be concluded that, with
FABLE 38
Typical Distribution of Impacts Occurring in a Railroad
Classification Yard
Impact Speed
be 1 ow 5 mph
at 5 mph
at 6 mph
at 7 mph
at 8 mph
at 9 mph
at 10 mph S over
Percent of Total Number of Impacts
Pullman Standard Data
36
3^
17
7
3
2
1
100%
Penn Central Data
}70
)7°
.17.^
6.0
3.1
2.3
1 .2
100.0%
Source: Technical Research Center, Penn Central Railroad
Company, "The Railroad Environment, A Guide for Shippers
and Railroad Personnel," Cleveland, 1966
88
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respect to stability, a solid waste bale should be
capable of withstanding at least one impact of 6 to 7
miles per hour during rail transport. In addition, the
bale should be capable of sustaining the "normal"
impacts occurring during shipment.
2. Lateral Shock and Vibration
Lateral vibrations frequently are caused by
out-of-phase vertical vibrations resulting from a
vertical out-of-phase movement of the springs and
wheels. They also may be excited by turnouts,
switches, rails out of alignment and/or worn truck
parts. Lateral vibrations are seldom due to curves.
Lateral vibration forces cause damage only in
special cases. Furthermore, lateral vibrations, strong
enough to cause an unrestrained package to merely
move from its position, occur for only 1 percent of
the total travel time under normal operating
conditions. However, packages with a center of
gravity higher than the width of their bases may be
damaged by the packages tipping over.
Lateral shocks generally result from forces
exerted in the vertical and longitudinal planes. In
almost all cases they have a time duration of less than
.02 seconds and are seldom severe. Due to the short
duration of these shocks, the normal protection
which is applied to the lading regardless of rail
transport considerations has proven to be sufficient,
as a rule, to guard shipments against lateral vibrations.
On the basis of the foregoing findings it can be
concluded that a relatively tight load is all that is
necessary to protect a load including bales against
lateral shock and vibration. Much will depend, of
course, on the smoothness or frictional surface
characteristics of the units in a given load. If the
surfaces of the packages or units are not slippery but
somewhat rough, then it is usually not required that
filler material be provided for those spaces of the car
width not occupied by the lading.
3. Vertical Shock and Vibration
Vertical vibrations are very seldom the cause of
damage to the lading if it is properly loaded.
Continuous vibration, at a force of about 0.25
percent of the weight of a package, will average about
3 to 8 cycles per second. Heavy loads, as a rule,
reduce the vibration rate to about 3 cycles per
second. Because of the resiliency of the springs
generally used, lightly loaded cars experience higher
vertical accelerations than cars loaded to their full
carry ing capacity.
The shock forces resulting from over-the-road
operations are rarely severe in the vertical plane. But
in yard operations these shocks may increase to about
double the normal force. Fortunately, vertical shocks
are of short duration lasting approximately .01
seconds.
However, vertical shocks gain significance in
terms of the height to which individual units are
stacked in or on a rail car. The lowest part of the
lowest package must be capable of carrying not only
the total weight placed on top of it but also the
dynamic load generated by this weight through the
vertical accelerations.
These findings show the importance of
determining the bale stability specifically with respect
to the height of loading during transport. Since the
maximum loading height of a rail car approximates 8
to 9 feet, and since the density of solid waste bales
including oversized items averages from 50 to about
80 pounds per cubic foot, it is desirable that the
lowest portion of a bale be capable of supporting
TABLE 39
Probability of Impact Occurrence in Sequential
Switching Yards
No. of
Yards
1
2
3
4
5
Impact Speed
to
5 mph
.700
.490
.345
.240
.168
over
5 mph
.300
.510
.655
.760
.832
over
6 mph
.126
.235
• 332
.416
.490
over
7 mph
.066
.128
.185
.240
.290
over
8 mph
.035
.069
.102
.133
.163
over
9 mph
.012
.024
.036
.047
.059
Source: Technical Research Center, Penn Central Railroad
Company, "The Railroad Environment, A Guide for Shippers
and Railroad Personnel," Cleveland, 1966
89
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about 720 pounds per square foot under transport
conditions.
If oversized wastes are excluded from the
compaction process, the compacted bales average 50
to 60 pounds per cubic foot after springback. In these
cases the lowest portion of the bale would, therefore,
have to carry only a maximum of about 540 pounds
per square foot under rail transport conditions.
Finally, the above findings suggest also that bales
in less than fully loaded cars are subject to more
severe transport conditions than those transported in
fully loaded cars. This fact must be remembered in
evaluating the shipment tests made during this
project, because none of the rail test cars was loaded
down to approach its load carrying capacity. Actual
rail-haul systems will, of course, operate with fully
loaded cars as much as possible.
4. Travel Distance and Time
The frequency of the application of the
destructive forces described above is closely
interrelated with the travel distance, other conditions
being equal. In addition, the effects of the force
application may also be influenced by the time
intervals occurring between the successive force
incidents. A sufficiently long time interval may, for
example, allow any recovery forces present to
become effective.
In current rail-haul analyses it is planned to ship
compacted solid wastes by rail over distances of
about 50 to 150 miles. At an average train speed of 25
miles per hour the bales would thus be 6 hours in
actual transport. This would be reduced to 3 hours if
the train speed were doubled. Freight trains travel
today, as a rule, at speeds between 25 and 50 miles
per hour. Consequently, for current
solid-waste-rail-haul systems, the bales should be
capable of surviving a rail transport of at least 150
miles distance and of 3 to 6 hours duration.
II. BALE STABILITY IN TERMS
OF MATERIAL HANDLING
Bale handling in solid-waste rail-haul will occur
almost exclusively at the transfer station and at the
disposal site. In each case, the operations concerned
require the following functions:
a. to pick up one, or more than one, bale;
b. to move the bale or bales; and
c. to deposit or drop the bale or bales at the
place of destination.
For such equipment as cranes, fork-lift trucks,
conveyors, slides, or manually operated tools, the
forces applied are primarily those of pressure, impact
and/or vibration. In principle, these forces are
identical to those encountered during rail transport.
The matenal handling equipment commonly used
is capable of meeting any requirements for the safe
handling of the items involved. Thus, material
handling equipment can be purchased readily to fit
the condition of the bale. However, this is not true
with respect to other phases of the operation. The
bale must and can be made to fit the transport
conditions encountered with commonly available
railroad freight cars, if specialized cars and transport
regulations are to be avoided.
It is reasonable to assume that a bale capable of
rail transport can also be handled successfully at both
the transfer station and the disposal site. This is based
on the fact that all goods damaged during rail
transport had been handled successfully before they
were placed on a railroad car. Similarly, a rail-haul
system for solid waste bales is apparently much more
demanding in the transport phase than in the few
material handling operations involved.
III. BALE STABILITY IN TERMS OF
BALE STORAGE AND SHELF LIFE
A rail-haul system for the shipment of baled solid
wastes may involve many operational variations.
These variations concern primarily the frequency of
bale pickup at the transfer stations. For example, it is
conceivable that from small transfer stations,
processing about 50 tons of solid waste per day, the
bales may be picked up only once or twice per week.
In contrast, large transfer stations will, in current
planning, receive a daily pickup service.
As a result, the age of the solid waste bales
shipped becomes significant. Assuming a maximum
24-hour transport time and a once-per-week pickup,
it is necessary that 8-day-old bales be suitable for a
150-mile transport. In turn, 9-day-old bales would
have to be suitable for the disposal site operations.
Any variations in the frequency of pickup
require, of course, that the bales be stored—probably
by stacking. However, this should not present
difficulties since the load put on the lowest bale in
storage is a static load rather than a dynamic load.
Thus, the load sustained in storage is less than the
load sustained by the lowest bale during rail transport
if the storage is 8 to 9 feet high.
Rail-haul loading considerations and perhaps even
the weight of the bales suggest that the height of bale
storage be limited to 8 to 9 feet. This implies that
storage shelves might have to be constructed, if a
higher stacking of the bale loading units is necessary.
This implies also that specific storage tests are not
required with respect to bale stability, if the bales
survive shipment tests which incorporate realistic
loading height conditions.
90
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IV. TEST SELECTION WITH RESPECT
TO BALE STABILITY REQUIRED FOR
SOLID-WASTE RAIL-HAUL SYSTEMS
The American Society for Testing and Materials
has established many methods for testing the strength
of materials and packages in terms of their
mechanical stability. These tests include static and
shock load capacity, drop, incline impact, and
vibration tests. Some of these tests require special
equipment such as a hexagonal revolving drum or
vibration tables. Others merely specify a particular
way by which a specimen is handled as, for example,
the roll-over test.
The information presented thus far indicates that
the impacts and vibrations generated during rail
transport are the major destructive forces which the
bale must sustain. Thus, within the scope of this
project it is of prime concern to test the rail transport
impact and vibration forces with respect to their
effect on the structural stability of the bale.
In this context it might be mentioned that any
minor bale deformation caused in storage or in
handling and transport is of less concern than the
structural stability, i.e., the cohesiveness of the bale.
First, the appearance of solid waste bales with respect
to their form is not critical. Second, the rail-haul
system can be designed, within the limits given in
Chapter II, to accommodate deformed as well is
non-deformed bales. Third, variations in volume and
shape of the bales must be anticipated within certain
ranges, depending upon the kind and condition of the
input materials. In terms of rail-haul, it is the
cohesiveness of the bale which represents one of the
key bale performance specifications.
The selection of the specific stability tests
conducted during the present study was made
primarily in consideration of the over-all time
limitations, the professional talent available, and
prudence in the expenditure of funds. On this basis it
was decided to obtain the necessary information on
bale stability by starting with selected exploratory
experiments on bales of a very broad variety, and by
designing each of the subsequent tests in the light of
the findings obtained through previous tests.
Following this approach, it was specifically decided
to conduct series of different but interrelated tests
including:
a. one series of vibration and impact tests
carried out under laboratory conditions and
involving bales of widely varying
characteristics,
b. two rail transport tests covering different test
conditions with respect to the bale type and
characteristics as well as the bale loading
configurations,
c. two sets of drop tests involving different
kinds of bales subjected to transport as well
as bales of varying ages after compaction,
and
d. a continuous observation of bale behavior
during the numerous bale handling
operations required at the test site.
Considering the nature, number, and variety of
the tests performed, and considering the scope of this
project, it can be concluded that the mechanical
stability of the compacted bales was ascertained on a
rather comprehensive scale. The composite
information obtained by these tests may be judged to
be at least adequate for the development of executive
decisions on the stability of the bales for rail-haul
operations.
SECTION THREE-VIBRATION AND IMPACT
TESTS MADE UNDER LABORATORY-SCALE
CONDITIONS INVOLVING TWELVE BALES
WITH WIDELY VARYING CHARACTERISTICS
The laboratory stability tests were conducted at
the Idea Center of Acme Products, a Division of
Interlake Steel Corporation. The Idea Center-a
certified National Safe Transit Committee laboratory-
emphasizes strapping research. It is equipped with
almost every type of strapping tool and test
equipment needed to ascertain the stability of
whatever item under a great variety of shipment and
material handling conditions. The professional
capabilities and the facilities of the Acme Center were
made available to the project without cost.
The objective of the tests described below was to
obtain, in an exploratory manner, indications of the
handling and transport stability of bales exhibiting a
selected set of widely varying characteristics.
I. THE TEST SETUP
In line with the above objective, the tests were
set up to yield criteria sufficient to guide both the
on-going bale development experiments as well as the
subsequent stability tests. Specifically, the tests were
designed to measure in broad increments the
resistance to destruction of various types of bales
compacted at different pressures and containing
loose, sacked, and shredded wastes. In addition, the
tests were designed to ascertain whether strapping of
the bales is necessary for rail-haul.
1. The Test Equipment and Basic Test Procedure
To test for the stability of the bales, it was
decided to subject each bale first to vibration impacts
and then to direct impacts of increasing force
application. As has been 'pointed out previously,
vibration impacts are by nature less severe than the
91
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direct impacts encountered in a rail-haul system. The
vibration tests were made on a Gaynes Vibrator and
the impact tests on an incline impact tester.
The Gaynes Vibrator simulates a railroad trip by
subjecting, the test specimen to a concentrated
number of vibration impacts, the strength of which is
related to the weight of the specimen. The simulation
is accomplished by vibrating the unit in such a
manner that the test specimen floats suspended at a
very small distance above the surface of the vibrator.
The test procedure requires that a sheet of paper
be placed under the test specimen and the vibration
cycles per minute be increased until the paper can be
moved freely beneath the load. In this condition, the
test specimen experiences a torce of one "g" or an
acceleration of about 32 feet per second.
To gain time, it was decided to vibrate two bales
simultaneously. However, since the bales were not of
equal weight, it was necessary to adjust the vibration
cycles to the vibration force requirements of the
heavier bale. As a result, the lighter bale always
received vibration impacts of a greater force than
indicated by the test results.
The Gaynes Vibrator was capable of simulating a
railroad trip of 1,000 miles in half an hour. However,
to utilize the available efforts best, it was decided to
simulate a rail trip of about 300 miles, which is twice
the maximum shipping distance currently considered
for solid-waste rail-haul.
The incline impact tester is also a very versatile
instrument. To obtain realistic impact ranges, the
incline was set at 10 degrees to the horizontal and the
accelerations were gauged to conform to rail
transport impact zone standards. To generate impacts
of increasing severity, the impact test sequence was
set as follows:
TABLE 40
Conbur Test
In evaluating the above impact sequence, it must
be recognized that impacts in Zone 3 constitute
"rough handling." Impacts in Zone 4 are frequently
classified in railroad operations as ''severe rough
handling" while impacts in Zone 5 approach the
magnitude of collision impact forces.
To ascertain the impact stability of the bales
under all—within reason—severe solid-Waste-rail-haul
operating conditions, it was decided to subject each
bale to the impact test series twice. Thus, each bale
received 12 consecutive impacts in the sequence
described in Table 40. The first six impacts were
applied in a direction parallel to the last compaction
stroke and the second six impacts were applied in a
direction perpendicular to the last stroke. In this
context it should be remembered that the highest
compression pressures were always applied during the
last compaction stroke.
2. The Bale Sample
The sample of bales used in this test series was
selected to provide the maximum amount of broad
guideline data possible under the existing operating
constraints. Accordingly, it was decided to include
two sets of bales compacted at gauge pressures of
about 2,000 and 3,500 psi. The bales were all made
from off-the-truck household refuse which was
compacted either as it was in the loose state,
contained in refuse collection paper sacks, or
shredded. Furthermore, one set of the bales of each
category was strapped and a corresponding set was
not strapped.
The shredded household refuse came from
Madison, Wis., where it was shredded in a
Heil-Gondard refuse size-reduction machine. The
other household wastes came from one single
Impact
Sequence
and
Number
1
2
3
k
5
6
Test Performance Specifications
1 ncl ine
(degree)
10
10
10
10
10
10
Length of
Incl ine
(i nches)
2k
30
36
k2
k8
58
Impact
Speed
(mph)
k ~ 5
6 - 7
6 - 7
8 - 9
8 - 9
8 - 9
Equ i valent
Rai 1 Transport
Impact Zone
Number
2
Low 3
3
Low k
4
5
92
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truckload of Chicago refuse. The Chicago refuse
contained a significant amount of spring
yard-cleaning materials as described in Chapter III
ot this report. All bales were produced the day before
the vibration and impact tests.
Concerning the strapped test bales, all strapping
was applied within 1 and 5 minutes after bale exit
from the press. Two straps were put on each bale in a
direction parallel to the direction of the last
compression stroke. After some exploratory
experimentation, it was decided to place the straps 4
inches from either end of the bale, leaving a distance
between the straps of about 15 inches.
The same type of commercially available straps
was used for each bale. This strapping is cataloged as
Interlake 5/8 x .020 inch Regular Duty Strapping and
has a tensile breaking strength of 1,440 pounds. The
strapping was applied with an Interlake Tensioner
Model No. B5F6, Sealer Model No. C1A5, and Seal
No. 51.
The total sample used for the laboratory
vibration and impact tests consisted of 12 bales. A
summary of the able characteristics is given in Table
41. The summary indicates that variations in both the
bale properties and bale production were duly
recognized in the makeup of the sample. For
example, one bale had a density of 50.76 pounds per
cubic foot and an over-all volume of 3.62 cubic feet,
while another bale of the same type and category had
a density of 70.68 pounds per cubic foot and an
over-all volume of 3.51 cubic feet.
II. THE TEST RESULTS
The results of the vibration and impact tests
performed at the Acme Idea Center are summarized
in Table 42. In the over-all, the data indicate that all
bales were exceedingly stable regardless of whether
they were strapped or not, or whether they were
compacted at lower or higher pressures.
The table also gives the over-all bale evaluation
ratings used. These evaluations were made by
observation and judgment and applied to all the bales,
not only during this stability test, but also during the
compaction experiments. The grades or ratings ranged
from "poor" to "very good." In making these
judgments, factors such as the following were taken
into account: compactness, sharpness of the edges,
loose portions, cracks, and appearance. It should be
highlighted that these evaluations rated the bales
relative to each other in terms of the total number of
bales made during the project.
A specific analysis of the foregoing data shows
that even the four bales, which were made from loose
household refuse of high dirt content and which,
moreover, were judged to be comparatively poor even
before the testing, :urvived both the vibration and
impact tests. These "our bales, considered the worst
bales of the lot, weie subsequently subjected to an
additional vibration test set up to apply vibrations
with a minimum force of one "g" until one of the
bales disintegrated.
This objective was achieved when Bale No. 1
(Test 5), the poorest bale of the sample, broke into
two sections, both of which had great spillage. The
application of the additional vibrations necessary for
the destruction of the first bale required 10 minutes at
195 cycles per minute. Thus, in terms of rail
transport, the additional vibrations represent a
shipping distance of about 330 miles.
As a result, the weakest bale of the total sample
was still capable of withstanding, before being
destroyed as a bale, a rail trip exceeding 600 miles.
This is four times the distance currently
contemplated for the rail-haul of solid waste. In
addition, the weakest bale was also capable of
surviving at least 12 impacts including two impacts
approximating collision force.
The other three bales made from loose refuse
remained quite stable in spite of this additional
330-mile trip. Bale No. 7, although not strapped and
only compacted at 2,000 psi, held well. The other
two bales, both strapped, survived the simulated
additional shipping distance in an even better
condition.
III. CONCLUSIONS
The test results support without any doubt the
conclusion that all the bales, without exception, were
extremely stable in terms of the total system
requirements for the rail-haul of solid wastes.
Actually all the bales exceeded, to a considerable
degree, the stability spe'cifications as developed in
detail at the beginning of this report section.
It was apparent that strapping improves, the
stability of the bales.
However, since the unstrapped bales withstood
the vibration and impact tests successfully, it was
decided not to conduct additional strapping tests
within the present project. It is understood that the
Acme Products Division of Interlake Steel
Corporation, is pursuing this matter further.
Finally, the vibration and impacts of the
magnitude applied in these tests appear not to lower
the evaluation grades as applied to the bales
throughout the stability test increments. A bale
judged "good" before testing tended, as a rule, to
remain in this category atter testing; and a bale
judged "poor" still survived all the tests in this
category.
In the over-all, the results of the laboratory tests
93
-------
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94
-------
Table 42. Summary of Results from the Vibration and Impact Test Series Conducted Under Laboratory-scale Conditions
TEST CHARACTERISTICS AND OBSERVATIONS
Bale Characteristics
Material
Compaction Pressure
Total Weight
Fortification
Vibration Characteristics
Time
Cycles per Minute
Equivalent Railroad Miles
Force Applied
Condition of Bale BEFORE Vibration
Overall Bale Evaluation
Specific Defects
Condition of Bale AFfER Vibration
Stability
Specific Defects
Overall Bale Evaluation
Condition of Bale AFTER 12 Consecutive Impacts
Applied in Two Identical Series of Six Impacts
Each Increasing in Acceleration from 4 to 1 1
Miles per Hour and in Distance from 28 to
58 inches
Stability
Specific Defects
Overall Bale Evaluation
Test Number 1
Bate No 1 1
Shredded
Madison, Wis
Household Ref.
2000 psi
239 5 Ibs
No strapping
9 minutes
215
300
One "g"
Very good
Many small cracks
parallel to 2nd ram
Stable
Some flakes dropped
off, cracks didn't
increase noticeably
Very good
Stable
Cracks become fis-
sures parallel to 2nd
ram ; appears as if
fissures affect only
one side, not deep
Good
Bale No 9
Shredded
Madison, Wis
Household Ref
3500 psi
22 1.5 Ibs
No strapping
9 minutes
215
300
More than one
"g"
Very good
Several cracks
parallel to 2nd
ram
Stable
Crack increase no
apparent , light
spillage
Very good
Stable
Cracks appeared
to open noticeably
but bale held well
Good
Test Number 2
Bale No. 10 Bale No 8
Shredded ' Shredded
Madison, Wis
Household Ref.
2000 psi
256.0 Ibs
Strapped
9 minutes
175
300
one "g"
Very good
A few small
cracks
Stable
Some flaking
on one side,
shght spillage
Very good
Stable
Droppings from
one corner and
side, still
strapped tightly
Good
Madison, Wis.
Household Ref
3500 psi
238.5 Ibs
Strapped
9 minutes
175
300
more than one
"g"
Very good
One major
crack, par-
allel to straps
Stable
Large crack did
not increase,
slight spillage
Very good
Stable
Some droppings
crack did not
increase pos-
sibly because th<
strapping might
have held pieces
together
Good
Test Number 3
Bale No. 13
Paper sacked
Chicago, 111
Household Ref.
2000 psi
167.5 Ibs
No strapping
9 minutes
175
300
more than one "g"
Very good
Bundle did bulge
and was not cubical
Stable
Some overall
growth
Very good
Stable
Very little spillage,
some growth
Very good
Bale No 5
Pip cracked
Chicago, 111.
Household Ref
3500 psi
194 5 Ibs
No strapping
9 minutes
175
300
one "g"
Good
Some skewing on
top surface, unlevel
Stable
Some skewed paper
on top surface
Good
Stable
Little spillage but
more growth on
skewed top
surface
Good
461-084 O - 72 - f
95
-------
Table 42. (continued) Summary of Results from the Vibration and Impact Test Series Conducted Under Laboratory-scale Conditions
TEST CHARACTERISTICS AND OBSERVATIONS
Bale Characteristics
Material
Compaction Pressure
Total Weight
Fortification
Vibration Characteristics
Time
Cycles per Minute
Equivalent Railroad Miles
Force Applied
Condition of Bale BEFORE Vibration
Overall Bale Evaluation
Specific Defects
Condition of Bale AFTER Vibration
Stability
Specific Defects
Overall Bale Evaluation
Condition of Bale AFTER 12 Consecutive Impacts
Applied in Two Identical Series of Six Impacts
Each Increasing in Acceleration from 4 to 1 1
Miles per Hour and in Distance from 28 to
58 inches
Stability
Specific Defects
Overall Bate Evaluation
Test Number 4
Bale No. 12
Papersacked
Chicago, 111.
Household Ref.
2000 psi
ITO.Olbs
Strapped
9 minutes
190
300
more than one "g"
Very good
Urutized weU with
strapping, loose paper
sack on top surface
Stable
Some growth perpen-
dicular to straps
Very good
Stable
No change
Very good
Bale No. 15
Pipetncked
Chicago, 111.
Household Ref
3500 pn
198.5 Ibs
Strapped
9 minutes
190
300
one "g"
Good
Tight bate, but
one strap applied
not quite perpen-
dicular to side.
appeared to spread
bundle apart
Stable
Some growth and
spread in middle
Good
Stable
Small increase of
spread at middle
Good
Test Number 5
Bale No. 7
Loose
Chicago, III.
Household Rel
2000 psi
183.5 Ibs
No strapping
9 minutes
190
300
one "g"
Fair
Appeared
loosely com-
pacted, con-
tained a lot of
dirt
Fairly stable
Some fluffing,
growth, and
spillage
Fair
Fairly stable
Bale appears
quite ragged,
some spillage
Fair
Bale No. 1
LOOM
Chicago, III.
Household Ref.
3500 psi
182.0 Ibs
No strapping
9 minutes
190
300
one "g"
Poor
Urutsble ap-
pearance con-
tained consider'
able dirt
Fairly stable
Quite a bit of
splflage and
loosening up
Poor
Fairly stable
tho loose bale
Bale began to
open up,
spillage
Poor
Test Number 6
Bale No 6
Loose
Chicago, 111.
Household Ref.
2 000 psi
248.0 Ibs
Strapped
9 minutes
190
300
one "g"
Fur
Some rebound aroum
straps
Fairly stable
Some fluffing.
spillaje, and rebound
Fair
Fairly stable
Some spillage;
strapping appears to
help in uratizing
Fair
Bale No. 18
LOOK
Chicago, 111.
Household Ref.
3500 pn
145.0 Ibs
Strapped
9 minutes
190
300
more than one "g"
Very good
None
Stable
Very little spillage
Very good
Stable
Some spillage
Very good
96
-------
TEST NO. 1
CONSISTENCY - SHREDDED
STRAPPING - NONE
Before Vibration
After Vibration
After Impact
97
-------
TEST NO. 2
CONSISTENCY SHREDDED
STRAPPING - 5/8 x .020 inches
After Vibration
Before Vibration
After Impact
98
-------
TEST NO. 3
CONSISTENCY - HOUSEHOLD IN PAPER SACKS
STRAPPING NONE
Before Vibration
After Vibration
After Impact
99
-------
TEST NO. 4
CONSISTENCY - HOUSEHOLD IN PAPER SACKS
STRAPPING - 5/8 x .020 inches
Before Vibration
After Vibration
After Impact
100
-------
TEST NO. 5
CONSISTENCY - HOUSEHOLD LOOSE
STRAPPING - NONE
Before Vibration
After Vibration
After Impact
101
-------
TEST NO. 6
CONSISTENCY HOUSEHOLD LOOSE
STRAPPING - 5/8 x .020 inches
Before Vibration
After Vibration
After Impact
102
-------
TEST NO. 7
CONSISTENCY - HOUSEHOLD LOOSE
STRAPPING - 2 STRAPPED (5/8 x .020 inches)
2 UNSTRAPPED
The bales pictured above were vibrated and impacted previously, i. e.
Test No. 5 - Bundles No. 7 and No. 1
Test No. 6 - Bundles No. 6 and No. 18
Test No. 7 is a photo before vibration to destruct
103
-------
appear to almost demand a second step in the
stability investigations, i.e., actual test rail shipments
involving a larger number of bales. Although the first
stability tests were extremely positive indeed, they
nevertheless were made on a laboratory scale not
fully representative of actual rail-haul conditions.
SECTION FOUR-FIRST 700 MILE RAIL
TEST SHIPMENT INVOLVING 40 BALES
WITH SELECTED CHARACTERISTICS
The first rail shipment test pursued a twofold
primary objective. The test was conducted (a) to
enlarge the number of observations made previously
on bale stability and (b) to do this in actual rail
transport.
I. THE TEST SETUP
The test setup was designed to take into account
a combination of factors including transport distance,
yard operations, loading configurations, and selected
variations in the bale characteristics.
1. Rail Equipment, Transport
Distance and Route
The bales were loaded on an old 55-ton
boxcar-40.6 feet long, 9.2 feet wide and 10.6 feet
high.
The car was moved by regular freight trains. The
transport distance exceeded 700 miles-shipment
being made from Chicago to Cleveland and back. The
route required the car to go through three railroad
yards. The Penn Central Railroad was asked to
subject the car to rough handling as much as
conveniently possible.
The car was equipped with an impact recorder
which was mounted on the car floor. This instrument
was attached to the car in Chicago and removed in
Cleveland. By that time it had registered more than 12
feet of chart. An example of a basic impact recording
chart indicating the impact interpretations is given in
Figure 23.
The chart in Figure 23 indicates that the
longitudinal impacts occurring in either direction are
registered and measured by moving the chart at a
controlled speed. The impact measurements are
plotted against time and thus facilitate the
identification of the place where a given impact was
sustained.
2. The Bale Sample
The sample used in this test consisted of 40 bales.
All 40 bales were made from regular Chicago
household refuse as it came off the truck. Together,
the 40 bales weighed about 5 tons or between 200
and 250 pounds per bale.
The test sample was designed to highlight four
different basic bale production characteristics. These
o
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REGISTER Co., CHAMPAIGN, /LUNO/S s-f-3?
FIGURE 23
Sample of Impact Register Chart Showing the
Interpretation Standards
104
-------
characteristics' pertain to the compaction pressures
used and to the nature of the household refuse before
compaction. Specifically, the test sample breaks
down as follows:
percent of the time the bales were in the railroad
environment. The transit time breaks down in three
segments as follows: (a) Chicago, Illinois - Elkhart,
Indiana--3.5 hours; (b) Elkhart - Toledo, Ohio--3.0
TABLE 43
Composition of Bale Sample for First Rail
Test Shipment
Nature of
Household Refuse
before Compression
Papersacked
Papersacked
Loose
Loose
Number of Bales
10
10
10
10
Compression
Pressures
(gauge psi)
2000
3500
2000
3500
The production of the 40 bales required almost
one full working week and thus the bales were 1 to 4
days old at the time of the shipment. None of the
individual bales or the bale sets were strapped during
the rail transport from Chicago to Cleveland and
back.
3. The Loading Configuration
The bales were placed on 3 x 4 foot pallets
immediately after compaction to facilitate trucking
from the test site to the rail car loading area.
Twenty-four bales were put on six pallets in single
layers, four bales per pallet. The remaining 16 bales
were stacked on two pallets in two layers or eight
bales per pallet. The bales, as illustrated in Figure 24
on the following page, were stowed in each corner of
the rail car, two pallets per corner. The two pallets
were stowed as close to each other as possible.
To simulate variations in the load, that a bottom
bale might have to carry during transport, it was
decided to burden some samples with a set of
sandbags weighing 30 pounds each. Specifically, one
single layer of eight bales in one corner was burdened
by a weight of 1 ton of sand per square yard. Another
single layer of eight bales in another corner was
loaded with 2 tons of sand per square yard. Including
the weight of the bale, this represents a static load on
the bottom of the bale of 280 and 500 pounds
respectively. All loads were, of course, secured by
bulkheads and bracing.
II. THE TEST EXECUTION AND RESULTS
The test car was 2 1/2 to 3 days enroute from
Chicago to Cleveland. However, the actual transit
time amounted to only about 9 hours or about 15
hours; and (c) Toledo - Cleveland, Ohio—3.0 hours.
The remainder of the time was spent waiting or in
classification yards.
During the more than 350-mile trip from Chicago
to Cleveland, the test car registered two longitudinal
impacts in Zone 3--exceeding accelerations of 6 miles
per hour, which is considered rough handling. In
addition, the test car sustained eight impacts in Zone
2. The distribution of the impacts was as shown in
Table 44.
In evaluating the data in Table 44 it should be
recalled, as outlined previously, that the probability
of a car being struck at speeds exceeding 6 miles per
hour is 1 in 3 if the. car passes through three
classification yards. Since the test car passed through
three classification yards, the results suggest that the
transport test conditions were, as requested, more
severe than those encountered normally in railroad
operations.
The over-the-road impacts which occur generally
from the run-in and run-out of slack in the car
coupling connections were all confined to Zone 1
during this test. This represents careful handling of
the cargo in transport and results from proper train
operation. No attempt was made to count the
number of Zone 1 impacts sustained during the
shipment.
The relationship of the longitudinal and vertical
shocks is shown in a selection of tape sections given
in Figure 25 on the following page. The tapes indicate
that most vertical shocks result, as outlined
previously, from longitudinal shocks. However, the
vertical shocks are, as shown, of short duration. They
generally last only for 0.01 seconds, while longitudinal
105
-------
"A"End
of Rai 1 roac
r
—
Ca
V
Pallet #3/single
layer
L 3500 L 2000
P 3500 P 2000
Weight
r
Pallet #l/double
, layer
1
P 3500 ' P 2000
-i
i
L 3500 L 2000
Pallet A/single
I layer
t
P 3500 jj> 2000
1
i
I
1
L 3500 [ L 2000
this side of car
»v3 ton
Pallet #2/double
I
i
i
L 3500 | L 2000
_ .. — _
1
1
i
i
P 3500 ' P 2000
i
DIRECTION OF
LOADING
i
^
^
/v 1 ton Refuse 1
j
i /
i
2 \/k
ton
2 ton Refuse ^nd \
| Ballast
1
V
L = Loose
P = Papersacked
106
-------
DIRECTION OF
LOADING
1
1
/
1 .00 ton Baled Refuse
4 -50 ton Sand Bal last
,v 5 -50 ton
\
/
1 .00 ton Baled Refuse
S2 .25 ton Sand Bal last
A/ 3 -25 ton
v
Pallet #7/single
1 layer
1
L 3500 L 2000
- - -- -
P 3500 P 2000
i
Weight this side (
~ 8 3/1* ton
Pallet #5/single
layer
P 3500 P 2000
L3500 | L 2000
i ' _1
3 - H
Pallet #8/single
1 layer
P 3500 P 2000_
1 3500 L 2000
I
3f car
Pal let #6/single
layer
1
L 3500 L 2000
P 3500 P 2000
k '
"B" End
Rai 1 road Car
FIGURE 24
Illustration of the Bale Loading Configuration
Used in the First Rail Test Shipment
107
-------
-r\>-
• Vertical
'. — Shocks
U* \ , fft
Longitudinal
Shocks
(1) Typical Over-the-Road Impact Recording
.
-A
-en
(2) Colehour Yard. Chicago, Illinois
FIGURE 25
Example of Impact Recordings Made During the First
Rail Test Shipment
108
-------
__cn_
cc ~~~
.- - V - - - •"'•"^- - _ - _
— >_
"L— -s
UJ'
ro
tri
ro
Vertical
Shocks
Long i tud inal
Shocks
(3) Elkhart, Indiana
— __ __ ___^— — — —~~~ —
*
( p
J - - Ou '
i _j n\ (*j -^ (Ji "!•*, »-' to
00^°° ^"" ^ o
' , 2"
- . - . . 4^ : —
f — —
o
c>
7
^
-^~,
. - cr> - '.'•',
Y^
tn . *-
0 '~^, 0
~— *
il --- .--
LO'
_i_
C4) Collmwood Yard. Cleveland, Ohio
FIGURE 25
Examples of Impact Recordings Made During the First
Rail Test Shipment
109
-------
shocks last, as a rule, for 0.1 seconds. The tapes show
that the vertical shocks were quite severe.
The car was first inspected in Elkhart, Ind.,
before it was humped in the classification yard. The
bulkheads and bracing were found to be broken and
the bales had shifted a few feet. Also, a part of the
sandbag loading ballast had been dislodged and
thrown throughout the car. No bale, however, was
destroyed or broken.
The car was again inspected in Cleveland by
members of the research staff of the Penn Central
Railroad. The cargo had not shifted further than was
observed at Elkhart. All the bales were found.in good
condition; not one bale had disintegrated or
crumpled. Some bales were steaming and their
outside temperature was estimated at 90 to 100
degrees Fahrenheit. The ambient temperature during
the trip was between 25 and 40 degrees F.
Subsequently, the car was rerouted to Chicago
for a final inspection of the bales. Impact
measurements were not taken during the return trip
which again required from 2 1/2 to 3 days in time. An
unknown number of additional impacts were
sustained by the test car during this trip.
The final inspection was made in Chicago by
members of the project team. It indicated that none
of the bales were destroyed. Even the two
second-layer front bales from Pallet No. 2 which had
fallen off and been thrown around in the car were
only partially damaged. All the other bales were
judged to be in very good, or at the very least, still in
acceptable condition.
down. This corresponds to the loading experience
gained from other rail shipments and reported at the
beginning of this section. It indicates that a
reasonably tight and confined loading reduces the
negative effects of impact and vibration generated
during transport.
The bales made from refuse in paper sacks
appeared, as a rule, to be in better condition than the
bales made from loose refuse. Only one paper-sacked
bale showed some separation between the sacks;
nonetheless, it was judged to be in "good" condition.
Finally, there was a relatively small amount of
spillage from the bales made from loose refuse. It is
estimated that the total spillage amounted to less
than 50 pounds or less than 1 percent of the total
weight of these bales. There was no spillage from the
paper-sack bales.
III. CONCLUSIONS
The above test results support the conclusion
that solid waste bales made from either loose or
paper-sacked refuse were extremely stable. All the
bales shipped appeared to exceed substantially the
stability required by most rail-haul systems as
currently contemplated.
It must be remembered in this context that
additional impacts of an unknown number and
magnitude were undoubtedly sustained during the
return trip of the test car from Cleveland to Chicago.
Considering the final results of this test, this fact can
only strengthen the certainty of the conclusions
drawn.
A selected number of the pictures taken during
the first rail shipment test are reproduced on the
following pages. The pictures show the test setup as
well as the condition of the bales after their return to
Chicago.
Furthermore, all the bales that were weighted
down by either sandbags or other bales appeared to
be in better condition than the bales not weighted
TABLE 4-f
Incidence of Longitudinal Impacts on Test Car During Transport
of Bales from Chicago to Cleveland in First Rail Test Shipment
Location of Impact Occurrence
Colehour Yard
Colehour Yard to Elkhart
Elkhart Yard
Elkhart to Toledo
Toledo area
Toledo to Collinwood, Cleveland
Collinwood Yard & area
Number and Strength of Impacts
Normal Yard
Operation
Zone 2
1
0
3
0
1
0
3
Rough
Handl ing
Zone 3
1
0
1
0
0
0
0
Severe
Handl i ng
Zone *t
0
0
0
0
0
0
0
110
-------
(48)
The boxcar used for the first rail test shipment
461-084 O - 72 - i
111
-------
(49)
Bales loaded down with sandbags , two tons of sand per square yard left and one ton per square yard right
112
-------
(50)
Bracing of the Bales Before Shipment:
(50) Bales Loaded Down with Sandbags
113
-------
(51)
Bracing of the Bales Before Shipment:
(51) Bales not loaded down
114
-------
(52)
Condition of the load after return to Chicago. Light line in left corner indicates height of sandbag pile.
115
-------
(53)
Condition of weighed down bales after return to Chicago. Notice small amount of spillage. Bales have expanded
to fill voids left by stacking.
116
-------
(54)
Condition of bales not weighed down after return tc Chicago. Notice small amount of spillage.
117
-------
(55)
Bales on truck after unloading of test car in Chicago. Notice condition of bales after more than 700 miles
of rail transport.
118
-------
SECTION FIVE-SECOND 700 MILE RAIL
TEST SHIPMENT INVOLVING 264 BALES
WITH SELECTED CHARACTERISTICS
The second and last rail test shipment made with
respect to this, as well as the APWA rail-haul project,
was designed to simulate actual solid-waste-rail-haul
shipment conditions as close as possible.
Specific credit must be given to the City of
Chicago, a participant in the APWA rail-haul project,
which enabled the project team to execute this vital
test, which might be considered the heart of the
stability investigations.
Without this second rail shipment test it could be
possible to judge all the previously reported stability
test results as being more indicative than definitive.
I. THE TEST SETUP
The second rail shipment test was set up in a way
similar to the first rail shipment test. With the
exception of a greatly enlarged scale, a similar
combination of transport factors were taken into
account.
1. Rail Equipment, Transport Distance and Route
The bales were loaded again on a boxcar.
However this car was 50 feet long, 9.2 feet wide, and
iO.6 feet high. The car was again moved by regular
freight trains and covered the same distance and route
as the first test car.
In addition to an impact recorder mounted on a
side wall, the car was also equipped with a humidity
and a temperature recorder.
2. The Bale Sample
As shown in Table 45 on the following page, the
264-bale sample was again structured to contain an
equal number of bales made from loose household
refuse and from household refuse placed in paper
sacks before compaction.
Furthermore, each of these two groups was made
up of a substantial number of bales compacted at
gauge pressures of about 2,500, 2,000 and 1,500 psi.
The results of compaction experiments conducted
just prior to the second shipment test had indicated
that compaction at pressures in the range from 1,500
to 2,500 psi might produce .significant over-all system
advantages.
Finally, each subgroup of samples was set up to
include bales of varying ages. Approximately 24
percent of the bales were more than 8 days old, about
48 percent were more than 7 days old and about 71
percent were more than 6 days old at the outset of
the test shipment. Correspondingly only 29 percent
of the bales were less than 6 days old and 52 percent
less than 7 days old. The variatious in bale age were
introduced to gauge the operational flexibility that a
solid-waste rail-haul system might be able to afford
with respect to bale pickup schedules.
3. The Loading Configuration
All 264 bales were stacked on pallets in four
columns stacked four high, totaling 16 bales per
pallet. Each stack of four bales consisted primarily of
bales having approximately the same characteristics,
e.g., four bales made from refuse placed in paper
sacks before compaction and compressed at 1,500
psi, or four bales made from loose refuse and
compressed at 2,000 psi, etc.
As shown in Table 46, the average weight of all
the bales is calculated to be 183 pounds. The average
weight of the bales calculated per pallet varied from
167.5 to 213.5 pounds. This implies that the bottom
of the lowest bale carried a load of about 670 to 855
pounds under static conditions and a higher load
under dynamic conditions.
The pallets were loaded randomly at both ends of
the car. The first eight pallets were placed at one end
and the other nine pallets at the other end of the car.
The loads at both ends were again secured by
bulkheads and bracing.
II. THE TEST EXECUTION AND RESULTS
Just as in the fjrst transport test, the car was
again 2 1/2 to 3 days enroute from Chicago to
Cleveland. However, this time the actual transit time
amounted to about 14.5 hours: Chicago to Elkhart,
Indiana, 5.5 hours; Elkhart to Toledo, Ohio, 5 hours;
and Toledo to Cleveland, Ohio, 4 hours.
During its more than 350-rn,ile trip from Chicago
to Cleveland, the car registered one impact in Zone 4
which, exceeding 8 miles per hour, is considered
severe rough handling. The specific distribution and
severity of the longitudinal impacts was as shown in
Table 47.
It might be recalled from the previous discussion
that the probability of a car being struck at impact
speeds exceeding 8 miles per hour is only 1 in 20 if
the car is handled in-three railroad yards. Considering
that impacts occurred in Zone 3 as well as Zone 4,
this test was fortunate in encountering transport
conditions more severe than those experienced in the
first rail test shipment. Thus, the test results must be
judged to be even more impressive than those
obtained previously.
Again the car was inspected in Cleveland by
members of the research staff of the Penn Central
Railroad. The bulkheads on one end of the car had
collapsed and some bales had spilled into the center
of the car. The bulkheads at the other end of the car
were damaged. However, all the bales were found to
be in good condition; not one bale had disintegrated.
119
-------
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-------
TABLE 46
Weight of Bales Shipped in the Second'Rail Transport Test
PALLET NUMBER
1
2
3
4
5
6
7
8
9
10
11
12
13
}k
15
16
17
TOTAL WEIGHT
of Bales
(16 un i ts per pa'i let)
(pounds)
3420
2920
3000
3220
3160
3120
2720
3020
2680
2840
2740
3100
2820
2780
2780
2840
1380 (8 bales)
TOTAL 48,5^0
AVERAGE WEIGHT
per Bale
(pounds)
213.75
182.50
187.50
201 .25
197.50
195.00
170.00
188.75
167.50
177-50
171.25
193.75
176.25
173.75
173-75
177.50
172.50
183.86
TABLE 47
Incidence of Longitudinal Impacts on Test Car During Transport
of Bales from Chicago to Cleveland in Second Rail Test Shipment
Location of Impact Occurrences
Colehour Yard
Colehour Yard-Elkhart
Elkhart Yard
Elkhart-Toledo
Toledo Area
Tol edo-C 1 eve 1 and
Col 1 i nwood Area
Number and Strength of Impacts
Normal Yard
Operat ion
Zone 2
0
0
1
0
0
0
1
Rough
Handl i ng
Zone 3
0
0
0
0
0
0
1
Severe
Hand 1 ing
Zone 4
0
0
0
0
0
0
1
Source: Technical Center, Penn Central Railroad
121
-------
The humidity indicator functioned for only
about 19 hours, i.e., until the ink was knocked from
the marking pen, apparently by coupling impacts.
The chart showed that the relative humidity rose
within the closed car from 85 percent to 100 percent
within 21/2 hours after the loading was completed.
The humidity then remained at 100 percent for the
remainder of the recorded time. It should be noted,
however, that it rained during the early part of the
shipment.
The temperature chart, as shown in Figure 26,
registered some high frequency pen vibrations caused
by car body motion. Ignoring these vibrations, the
chart shows that the car air temperature ranged from
70 degrees to 95 degrees Fahrenheit. Temperature
maxima were registered just after noon of each of the
5 days of record-taking.
To put the temperature and humidity data into
some perspective, it is necessary to consider the
weather conditions prevailing in the total test area
during the test period. The general temperature and
humidity readings for Chicago and Cleveland were as
shown in Table 48.
In analyzing the data in Table 48 it must oe
recognized that the bale production for this test
started on April 28, 1969 and that the transport
movement itself began in the afternoon of May 8,
1969. A general comparison between the
measurements taken inside the test car and those
established by the U.S. Weather Bureau indicates that
the bales produced a significant amount of both heat
and moisture. These findings indicate that some
degradation of the organic constituents of the bales
took place during transport and that the
decomposition was most likely aerobic.
The data, however, do not lend themselves to a
quantitative evaluation of the biological activity ir
the bales. Furthermore, these data are not, by
themselves, adequate for the establishment of
quantitative inferences concerning all the rail-car and
transport requirements. Factors such as the type of
car and car enclosure, the tightness of the doors, the
FIGURE 26
Record of Air Temperature in the.Test Car
During the Second Rail Test Shipment
Source: Champ Carry Technical Center, Pullman Standard,
Division of Pullman, Incorporated
122
-------
cooling effects of prevailing winds, and the air speed
during transport, would need further investigation.
Nevertheless, the available data can be considered a
good indicator of some-significant conditions which
must be recognized in the rail-haul of solid wastes.
Combined with the total information developed
during this project, the data are judged to provide a
basis sufficient for the establishment of the initial
specifications for rail-haul demonstration projects.
Finally, the return trip of the car from Cleveland
to Chicago required again 2-1/2 to 3 days in time.
Although impact measurements were not taken
during that time, it is clear that impacts did occur. In
the over-all, all bales again came back intact and the
amount of spillage was estimated again at less than 1
percent of the weight of the loose bales.
Ill CONCLUSIONS
Considering the lading configuration, specifically
the height of the lading, and the severe handling of
the test car, railroad experts regard the test results as
adequate proof of the excellent stability of the
compacted bales. In their judgment bales of type and
kind tested will be acceptable for shipment by any
railroad.
This conclusion was already reached by the rail
shipment experts after completion of the shipment
from Chicago to Cleveland. Since the bales remained
intact even after the additional Cleveland-Chicago
return trip, it is clear that the stability of the bales
must be considered excellent indeed.
Finally, the bales are capable of developing a
significant amount of heat and moisture during
transport. This possibility must be taken into account
in the selection of rail rars as well as in the
establishment of bale storage facilities desired at the
transfer station or the disposal.site.
A selection of pictures taken during the second
rail test shipment is presented on the following pages
to convey, visually, the extraordinary stability shown
'by the bales used.
TABLE 48
Selection of Local Climatological Data for Chicago
Illinois and Cleveland, Ohio for Time Period
April 28, 1969 to May 15, 1969
Date
Chicago
Temperature
High Low
1969 °F. °F.
4/28
4/29
4/30
5/1
5/2
5/3
5/4
5/5
5/6
5/7
5/8
5/9
5/10
5/11
5/12
5/13
5/14
5/15
54 39
51 36
62 37
73 47
85 56
82 54
83 56
79 62
81 65
76 57
70 51
58 47
52 42
58 42
63 40
67 45
73 49
79 52
Humidity
High Low
% %
86 76
76 36
76 37
71 31
53 21
77 42
72 29
67 45
84 44
87 37
86 51
86 53
86 54
73 38
82 34
86 50
93 30
74 45
Ra i nfal 1
( inches)
0.19
0.00
0.00
-
-
T
T
T
.06
,28
.48
.28
.58
.08
T
0.00
0.00
T
Cleveland
Temperature
Hiqh Low
°F. °F.
Humidi ty
Average
% \
79 54
56 38
54 38
53 39
55 39
68 39
64 47
67 39
58
43
43
35
36
40
41
38
Rainfal 1
( inches)
.76
.17
.62
.36
.00
.02
T
.00
T = Thunderstorm
Source: U. S. Department of Commerce, Weather Bureau
123
-------
:f
(56)
(57)
(58)
Bales before the second, more than 700 mile rail test shipment. Notice space left due to stacking on pallets
which causes instability of the load and therewith more severe test conditions.
124
-------
(59)
(60)
(61)
Condition of load after return to Chicago in second rail test shipment.
125
-------
(62)
(63)
(64)
(65)
Condition of load after return to Chicago. Notice small amount of spillage. Paper-sacked refuse bales
to be in excellent condition.
appear
126
-------
(66)
(67)
(68)
(66) Loose Refuse Bales Survived the Test Quite Well.
(67) Unloading of Loose Refuse Bale.
(68) Unloading of Bales, Notice Form of Bales Left After Rough Unloading Procedure.
461-084 O - 72 - 10
127
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SECTION SIX-THE DROP TEST SERIES
COVERING, IN 18 TESTS, 46 BALES
WITH VARYING CHARACTERISTICS
Although the vibration and impact tests showed
that the solid «vaste bales were extremely stable, it
was decided to conduct a series of drop tests in order
to augment the available information on the
structural stability of the bales. The drop test were
made either at the test site or at the Idea Center of
Acme Products Division of Interlake Steel
Corporation.
In total, 46 bales were selected at random and
subjected to drop tests in 18 separate test operations.
The major test variables concerned (a) bale
characteristics, in particular bale age; (b) the height
and number of drops; and (c) operationally oriented
drop conditions such as the number of bales dropped
simultaneously. The individual bale and test
characteristics and the test results are summarized in
Table 49 presented on the following pages
In evaluating the data in Table 49 it should be
highlighted that the height of the drop amounted
usually to about 9 or 10 feet. Only two drops were
made from a height of 5 feet. Although it is not
anticipated that rail-haul systems will be designed to
require dropping of the bales in regular operations it
must be recognized that drops might occur
accidentally.
In the overall, the drop test results complement
the findings presented previously on the other
stability tests. Solid waste bales, which appear stable
after exit from the press, are capable of taking a
considerable beating from drop impacts. This holds
true regardless of whether the bales are dropped
individually or in groups. However, it appears that
bales produced at higher compaction pressures are
more resistant to drop impacts than, as expected,
bales produced at low compaction pressures.
The drop tests confirm on their own and in their
own way all the conclusions drawn previously. Solid
waste bales which appear to be acceptable after
leaving the compaction press will also meet all the
stability requirements of currently contemplated
rail-haul systems.
A selection of pictures taken during the drop
tests is given on the following pages.
SECTION SEVEN-OBSERVATION OF BALE
PROPERTIES DURING THE NUMEROUS
BALE-HANDLING OPERATIONS
REQUIRED AT THE TEST SITE
The operations at the test site required that each
bale be handled many times. Specifically, each bale
had to be (a) removed from the press after
compaction, (b) transported to the scale in the
bucket of a front-end loader, (c) placed on the scale
and removed after weighing, (d) transported again in
a front-end loader to an interim storage place inside
the building, and there (e) put on the floor of the
building or on a table. In addition, the test operations
often required that the bales be shifted around within
the building so as not to interfere with the
experiments going on.
Moreover most bales were transported to the
outside of the test building and stored there for a
considerable length of time for observation.
Observations of bale appearance and stability and
attempts to manually remove apparently loose
portions of the surfaces and corners, were made at
random throughout the test period.
The numerous observations throughout the
10-week test period can be summarized as follows:
1. Bales that appear cohesive after exit from the
press can be handled without special
precautions.
2. Even bales exhibiting apparently significant
structural defects are still surprisingly strong
in terms of the bale handling operations
performed.
3. Exposure of bales for about three weeks to
outside weather conditions during February
to May 1969, did not cause an appreciable or
obvious amount of structural deterioration.
4. Spillage, as a rule, amounted to less than 1
percent of the weight of the bale.
The above observations, although not
documentable in terms of specific measurements, are
presented to enhance the test results given on bale
stability. In combination with the findings presented
previously, they support the conclusion that bale
handling needed at the transfer station, will not be a
source of significant difficulties.
SECTION EIGHT-MAJOR CONCLUSIONS ON
THE STABILITY OF COMPACTED
SOLID WASTE BALES
A highly significant number of bales produced
during this test program and representing a great
variety of bale characteristics were subjected to a
broad series of relatively severe stability tests.
The test results, taken in combination, indicate
that solic' waste bales are surprisingly stable. Bale
failure under test conditions which surpassed
substantially all the current requirements for
solid-waste rail-haul was extremely rare.
Bales produced at compaction pressures in the
range from about 2,000 to 3,500 psi did not appear
to require special care with respect to rail transport or
material handling. In the over-all, bales made at these
128
-------
pressures from either loose or shredded refuse or
from refuse placed in paper sacks performed
exceedingly well.
Finally, as indicated in Section One of this
chapter, the bales subjected to the tests must be
considered, for practical purposes, as being at
equilibrium with respect to their internal cohesive
and expansive forces. Most of the spnngback activity,
which occurs within the first 5 minutes after bale exit
from the piess, had already taken place in some cases,
long before any of the stability tests were made.
Thus, it can be concluded that solid waste bales
exhibiting a stable appearance after exit from the
press are, as a rule, suitable for the transport and
material handling operations of rail-haul systems as
currently contemplated.
129
-------
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TESTS NO. 9 AND NO. 8
CONSISTENCY - SHREDDED
STRAPPING - TEST NO. 9 NONE
TEST NO. 8 - 5/8 x .020 inches
After Two Drops
TESTS NO. 10 AND NO. 12
CONSISTENCY HOUSEHOLD LOOSE
STRAPPING - TEST NO. 10 - NONE
TEST NO. 12 - 5/8 x .020 inches
After One Drop
After Two Drops
132
-------
TESTS NO. 13 AND NO. 11
CONSISTENCY - HOUSEHOLD IN PAPER SACKS
STRAPPING - TEST NO. 13 NONE
TEST NO. 11 - 5/8 x .020 inches
After Two Drops
133
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-------
CHAPTER V
THE IMPLICATIONS OF APPLYING HIGH PRESSURE
COMPACTION TO SOLID WASTES FOR
RAIL-HAUL AND SOLID WASTE DISPOSAL
This chapter takes up the implications of
applying high pressure compaction to solid wastes for
rail-haul as they relate to the development of suitable
compaction equipment and major rail-haul system
building blocks. As outlined in the APWA rail-haul
interim report, the major building blocks of the
system are (1) the transfer stations, (2) the transport
link, and (3) the sanitary landfills.
In analyzing these implications, it must be
recognized that they are to be dimensioned within
the scope of two different projects. This report
emphasizes the compaction-oriented implications.
The report on the first phase of the rail-haul
feasibility study deals in detail with the rail-haul
system implications.
The high pressure compaction of solid wastes is
expected to have implications far beyond the scope
of solid-waste rail-haul. Thus, to put the results of
this project into some perspective in terms of total
solid waste disposal problem, it was considered
appropriate to indicate some of the non-rail-haul
implications and promises as well.
SECTION ONE-THE DEVELOPMENT
OF COMPACTION EQUIPMENT
PERFORMANCE SPECIFICATIONS
Acceptable equipment performance
specifications have to be reasonable in terms of the
technical requirements as well as the cost incurred in
meeting those requirements. Today's technology has
demonstrated quite clearly that almost any technical
objective can be achieved if cost, relative economics,
and allocation of resources are not restraints.
However, to develop compaction equipment
specifications for the reality of solid wastes disposal,
which is quite sensitive to costs, it was necessary to
keep in mind the cost-performance factors associated
with alternative specifications. In terms of
compaction technology, this implies that attention
should be given the low pressures of a given pressure
range, to a reasonable size of the bale in the
compaction chamber, to a low weight/force ratio of
the press frame, to machinery requirements, and to
cycle speeds and sequences.
To perform the investigations concerned in a
reasonable manner requires the establishment of
criteria for a'comparison of different compaction
press systems. Unfortunately a comprehensive
comparison represents an undertaking far beyond the
limited scope of this project. It must be highlighted in
this context that an investigation of alternate press
performance specifications necessitates many analyses
of numerous relationships between a large number of
variables which are, in themselves, extremely
complex.
Thus, the decision had to be made to confine the
project efforts in this area to tentative, exploratory
investigations aimed at the development of indicative
rather than definitive guideline information.
I. GUIDELINES FOR THE
INVESTIGATION OF ALTERNATE COMPACTION
EQUIPMENT SPECIFICATIONS
To guide and also to confine the study team
efforts within the scope of available resources, it was
necessary at the outset to establish selected
constraints. To meet the project deadlines, however,
these constraints had to be fixed before completion
of the compaction experiments. Thus, the guidelines
had to cover the problem of performance
specifications in broad terms.
The specific guidelines used for this part of the
study effort were as follows:
Characteristics of the material:
Heterogeneous mixtures of varying moisture
contents which could behave like semi-solids
under compaction, and exhibit springback
characteristics instantaneously after release of
pressure
Moisture content:
20 to 40 percent by weight of the input material
mixture
Precompaction of input materials:
No precompaction of input materials other than
that produced by collection trucks of the type
now commonly used by municipalities.
Productivity
50 to 1,000 tons of solid waste per 8-hour shift
Cycle operating rate:
0.3 to 2.0 bales per minute, excluding any
holding time of the final pressure applied
Total cycle rate:
Cycle operating rate plus a maximum of one
minute of final pressure holding time
135
-------
Compaction pressure applied:
2,000 to 3,500 psi without holding time, 2,000
psi and below with a maximum final pressure
hold time of 1 minute
Material density in the compaction chamber:
Range of 70 to 90 pounds per cubic foot, average
1 ton per cubic yard (74 Ibs/cuft)
Volume reduction ratio:
At least 15:1 , preferably 18:1
Bale shape in the compaction chamber:
Cubic, rectangular or cylindrical
Bale size in the compaction chamber:
0.25 or 0.3 to 1.0 cubic yard
Stability of the bale:
Except for bales made from refuse delivered
during heavy rains, almost all bales are stable
after release of pressure
Basic process operations:
Uninterrupted, separate processing of each
individual input charge regardless of the number
of compaction stages. One bale is always
produced per run from a single solid waste input
load charged in one step
Feeding:
A full charge always fed into the charging box,
no additional feedings of input materials during
individual compaction runs
Type of compaction equipment:
Hydraulic presses
Useful service life of the equipment:
10 to 20 years at 5 days per week and 6 to 8
hours per day
Equipment cost:
Low-cost application of existing compaction
technology is of key importance
In evaluating these guidelines plus the findings of
the subsequent investigations, it must be stressed that
they purpose to deal only with a very preliminary,
conceptual value-engineering analysis. It should be
recognized in this context that: (a) The design of
existing metal scrap balers is often estimated to cost
about 3,000 hours of engineering; (b) the design of
completely new types of equipment requires more
and perhaps different effort, and (c) the task at hand
had to be tailored to the resources available.
It is obvious, of course, that the guidelines could
be enlarged in number and be more detailed or
stringent in content. It also is obvious that further
work in equipment development, will modify the
constraints and will elicit results which this project
can only hypothesize.
Finally, to be on the safe side, it was decided to
set some constraints to exceed the performance
specifications outlined in Chapter II of this report. As
a result, the investigation of high pressure compaction
for the rail-haul of solid wastes also provides
information which points to potential applications in
other phases of the solid waste disposal field.
II. PRESS CAPACITY CONSIDERATIONS
The constraints influencing the press capacity are
interdependent. The press capacity is determined by
the interrelationship between the total throughput
tonnage, the bale size, and material density in the
compaction chamber, and the rate of bale
production.
1. Press Productivity in Terms of the
Interrelationship Between the Bale Size and Material
Density in the Compaction Chamber and the Rate of
Bale Production
The interrelationship between throughput, bale
size, material density, and rate of bale production is
shown graphically in Figure 27. Both the total tons of
waste compacted, as well as the number of tons
handled per minute, are shown together on one axis
and the number of bales per minute on the other axis.
The relationship between bale size and bale weight in
the compaction chamber was set for 1 ton to equal 1
cubic yard.
Figure 27 can be regarded as a graphic matrix for
determining some of the specification alternatives
resulting, not only from variations in the over-all
production rate, but from tradeoffs between bale size
and production rate. A 240-ton over-all throughput,
for example, can be achieved with two 0.25-cubic
yard bales per minute, one 0.50-cubic yard bale per
minute, or one 1.0-cubic yard bale every 2 minutes.
Conversely, a 480-ton throughput cannot be
achieved with a single, 0.25-cubic yard compaction
chamber press. This throughput would require two
presses of that size, and both presses would have to
operate continuously at maximum speed.
The matrix appears to be a versatile tool for
identifying the bale size or production rate
alternatives in terms of an equal over-all performance.
In turn, these alternatives suggest tradeoff
opportunities between the bale size and the rate of
bale production, and the way these two factors may
be balanced against each other if additional press
design considerations are taken into account.
2. The Effects of Pressure
Hold Time on Production
The production effects of variations in the
pressure hold time from 15 to 60 seconds are
illustrated in Figure 28. The pressure hold times
indicated do not, of course, include the time
136
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1.0
1.5 2.0 2.5
Total Cycle Time in Minutes
3-0
'Examples referred to in the text.
FIGURE 28
The Influence of Pressure Hold Time On
the Production Rate
the production rate, i.e., the number of bales made
per minute, or a combination of both. For example, a
decrease in the production rate by 50 percent can be
offset by an increase of 50 percent in the bale size.
3. Options Concerning Bale Size and Compaction
Rates in Terms of Varying Production Requirements
per 8-Hour Shift
Table 50 on the following page presents a matrix
for the selection of bale size in the compaction
chamber and the corresponding compaction rates for
throughput requirements ranging from 50 to 500 tons
per 8-hour shift.
The compaction rates are expressed in terms of
the active or direct cycling operation time required
and are stated as rate per minute. The active or direct
cycling rate per minute gives the time span within
which the press would have to perform all major
compaction movements or steps. Accordingly, this
rate determines the speeds at which all the major
individual compaction functions would have to be
performed. Examples of such functions include: the
loading and the closing of the charging box, the
movement of the rams in multi-axis compaction
devices excluding the pressure hold, the ejection of
the bale, and the return of all elements to their zero
position.
The active cycling rates given in Table 50 are
adjusted to show the effect of hold time varying from
0 to 60 seconds. The addition of a pressure hold time
decreases, of course, the time available for the active
cycling operations, if the over-all production
requirement is kept constant.
138
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The total amount of time available for the
production per bale, i.e., for the total cycle including
any hold time, is given in Table 50 in the fourth
column headed "@0 sec. hold." The data are
expressed in the decimal system. Thus, a value of 2.4
minutes is the equivalent of 144 seconds or 2 minutes
and 24 seconds.
The time span in Column 4 is determined by
dividing the total production time by the number of
bales to be produced per shift. This span represents
the total cycling time available. It does not change
regardless of the relationship that might be found
between the portions of active cycling time and hold
time, provided a pressure hold is applied. If no such
hold is applied, the total cycling time is equal to the
active cycling operations time.
In evaluating the data given in Table 50, it should
be recognized that they are calculated on the basis of
an effective working time of 480 minutes per 8-hour
shift. This base was chosen to show the maximum
production achievable.
The data underlined in the table indicate the
interrelationships which fall within the limits of the
guidelines established for this study. They show, for
example, when and under what specific operating
conditions it is possible to accommodate a given
amount of pressure hold time. They also show the
variations possible in the corresponding sizes of the
bale in the compaction chamber as well as the
corresponding number of bales which must be
produced under the conditions given. Conversely, the
data not underlined represent operating speeds which
allow either less than 30 seconds or more than 3
minutes for the accomplishment of all the required
major compaction movements or steps.
To facilitate a realistic selection of press capacity
for rail-haul and other applications, it is necessary to
adjust the nominal press capacity downward to more
practical production levels. Within the scope of this
project, it was decided to follow the guidelines
outlined in Chapter I! of this report. It might be
remembered that those guidelines suggest an effective
working time of 360 minutes per 8-hour shift. Thus
the actual rate of production is pegged at 75 percent
of the nominal press capacity.
Table 51 on the following page presents a matrix
similar to the one shown in Table 50 but based on an
effective working time of only 360 minutes per
8-hour shift. Combined, the data in both tables
indicate that a substantial degree of operational
flexibility is provided for the actual day-to-day
execution of the compaction process. This holds true
specifically if the presses are designed to serve the
100 and 250 tons per 8-hour shift production
requirements. Considering the value of pressure hold
time for the compaction of wet and/or dry and
difficult-to-compact materials, this flexibility may be
needed to assure successful year-round compaction
operations.
Furthermore, the data presented in both tables
indicate that a wide choice is given for the selection
of tradeoffs. In particular, significant tradeoffs appear
to be available with respect to the size of the
compaction chamber and the use of pressure hold
time.
A 100-ton per 360 minutes process throughput
requirement, for example, could be achieved
satisfactorily with bale sizes ranging in the
compaction chamber from 0.25 to 0.75 cubic yard.
Furthermore, a press compaction chamber for a bale
of 0.50 or 0.75 cubic yard could, under the same
throughput condition, accommodate a holding time
up to 1 minute. Such a hold time, as reported in
Chapter III, could substitute for about 500 to 750 psi
of applied pressure and reduce, in turn, the press
construction requirements resulting from the
specifications of a given face or applied pressure. As
will be shown, both the size of the compaction
chamber and the amount of face pressure required are
in addition to the speed of operations, major factors
in shaping the cost of high-pressure compaction.
Over-all, the data indicate that series of alternate
performance specifications appear suitable for
operations within the guidelines and constraints
given. However, since each individual specification
carries different implications for both the process
cost and operations, it is necessary to tailor the
requirements to the local needs. Thus, individual
press performance specifications must be based on
local operating conditions as well as the
characteristics of the materials to be compacted and
the influence of the wet and dry days encountered.
4. Press Capacity in Terms of Transfer Stations
for the Rail-Haul of Solid Wastes
Disregarding special local conditions, the above
information can be used to indicate in broad terms
some of the basic configurations for using high
pressure compaction of solid wastes in selected
rail-haul transfer stations. These basic configurations
are based purely on one-shift operations which
furthermore are pegged at only a 75 percent level of
efficiency.
a) 50 tons per 8-hour shift capacity
Without necessitating high compaction rates, the
50-ton station can be served by one press having a
bale volume of 0.25 cubic yard in the compaction
140
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141
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chamber.
Furthermore, a pressure hold time ranging from 0
to 60 seconds could be accommodated without
difficulty.
A 0.50-cubic yard bale size compaction chamber
press might be suggested for this capacity transfer
station if pressure holds of 45 or 60 seconds were to
be applied.
b) 100 tons per 8-hour capacity
A 100-ton station appears to be especially well
served by presses with bale sizes of 0.50 or 0.75 cubic
yard in the compaction chamber. In both cases a
pressure holding time from 0 to 60 seconds could be
provided.
The use of a 0.25-cubic yard compaction
chamber bale would require relatively high speed
press operations and be limifed to not more than a
15-second pressure hold.
In contrast, a 1 cubic yard bale-compaction
chamber press could be used for relativley slow
operations. However, the selection of such a press
only appears to be reasonable in terms of the data
presented if a pressure hold of 45 or 60 seconds is
contemplated.
c) 250 tons per 8-hour capacity
A 250-ton station requires that the volume of the
bale in the compaction chamber be not less than 0.50
cubic yard.
If pressure hold times of 15 or 30 seconds are
desired, then the compaction chamber bale volume
would have to be 0.75 cubic yard.
A pressure hold time of 45 seconds requires that
the bale have volume of 1.0 cubic yard in the
compaction chamber.
A pressure hold time of 60 seconds cannot be
accommodated within the operational constraints
given for the analyses of this study.
d) 500 tons per 8-hour shift capacity
A 500-ton station can be served only by presses
operating at the comparatively high speeds of 0.54 or
0.72 minute per total cycle. At this speed the
production rates would be equivalent to an output of
one to two bales per minute. The corresponding bale
volume in the compaction chamber would have to be
0.75 or 1.0 cubic yard, respectively.
If any pressure hold-time were to be applied, a
500-ton station would have to be served by multiple
compaction units. For example, two presses as
indicated for the 250-ton transfer station throughput
requirements, or five units as indicated for the
100-ton process throughput, could substitute for a
single 500-ton per 8-hour shift press.
The 500-ton compactor represents the largest
single unit possible on the basis of the bale sizes and
compaction rates called for in the guidelines.
5. Conclusions
In terms of the total set of transfer stations
investigated for the rail-haul of solid wastes, the 100-
and 250- ton presses appear to provide a maximum of
operational flexibility if a nominal 8-hour throughput
is to be processed within 6 hours.
Thus, since the number of potential applications
is quite large in the 100- to 250- ton 8-hour shift size
range, it appears that prime emphasis should be given
the development of presses with a 0.50- and/or
0.75-cubic yard bale size in the compaction chamber.
Selection of this size press implies that very high
volume transfer stations would be served by more
than a single compaction unit. It is not necessary in
such cases to plan for any backup or standby units
since the basic operations are based on just one
8-hour shift per day and, in addition, at an efficiency
level of only 75 percent of the rated capacity. Any
equipment breakdown or operational delays could
therefore be handled easily by a temporary speedup
of the operations, overtime schedules or, at worst by
a second shift.
III. HYDRAULIC PRESSURE CONSIDERATIONS
In order to gauge the effects of variations in the
face pressure applied, it is necessary to investigate
some factors which are important in the utilization of
hydraulic pressures. The factors considered here
concern (a) the availability of hydraulic components,
(b) the consequences of unit pressure variations with
respect to the size of the hydraulic rams and
cylinders, and (c) the use of hydraulic forces in the
compaction of solid wastes.
It should be emphasized that this section of the
investigation is based on the assumption that the first
solid waste presses would operate primarily by
hydraulic means of pressure generation and
transmission. This assumption appears to be justified
by the process implications resulting (as outlined in
Chapters II and HI) from the compaction behavior of
the solid waste input materials usually encountered in
municipal refuse collection.
1. The Availability of Hydraulic Components
and Parts
A brief survey of the utilization of hydraulic
components, including pumps, pipes, valves,
accumulators, and fittings, indicates that most heavy
press manufacturers design their equipment to
operate at hydraulic pressures of 3,000 to 3,500 psi.
According to the "Fluid Power Handbook and
Directory," compiled by the editors of "Hydraulics
142
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and Pneumatics" magazine, this range of pressures
apparently represents the highest level of pressures
for which the necessary components are considered
more or less staple items and are most widely
available.
Of course, hydraulic components are made for
operations requiring higher hydraulic pressures.
Specifically, there appears to be a trend toward use of
5,000 psi hydraulic pressure systems. Hydraulic
systems operating at even higher pressures are in
existence but are not recommended for the normal
production line operations requiring both heavy duty
service and a high level of reliability.
In accordance with these findings, it was decided
to base the explorative investigations on utilization of
hydraulic pressure systems operating at 5,000 psi or
less.
2. The Relationship Between the Diameter
of the Hydraulic Cylinder and Variations
in the Pressure Applied
To keep the following investigations within
manageable proportions, it was decided to base all
calculations on the two bale/compaction chamber
sizes identified above—0.50 and 0.75 cubic yard.
Bale volumes of 0.50 and 0.75 cubic yard in the
compaction chamber are equivalent to roughly 13
and 20 cubic feet respectively. If the bale were to be
a cube, these volumes, in turn, would identify the
lengths of the sides as 2.35 or 2.71 feet respectively.
As a result, the relevant compaction pressures would
have to be applied to an area of 5.52 or 7.34 square
feet.
Four levels of hydraulic pressures and three levels
of applied pressures were considered. The hydraulic
pressures ranged from 1,000 to 5,000 psi and the
applied pressures from 1,000 to 3,000 psi.
The interrelationship between hydraulic cylinder
or ram area, hydraulic pressure, and pressure applied
is, in terms of the above sets of values, graphically
presented in Figure 29 on the following page. The
area of the hydraulic ram is given by the relationship
where A^is the hydraulic ram area, Ac the
compaction area, Pc the compaction pressure and P^
the hydraulic ram pressure.
The data do not reflect the effects of pressure
hold time. An example of the pressure hold effect on
the ram diameter is shown for the 0.75-cubic yard
compaction chamber bale and a hydraulic pressure
level of 3,000 psi. It might be remembered that a
pressure hold may be used as a substitute for 500 to
750 psi in applied pressure.
The curves suggest that diameters of the
hydraulic cylinders might need to be very large,
depending on (a) the amounts of hydraulic and
applied pressures used and (b) their pressure
correlations. This finding is predicated on the
assumption that a single cylinder delivers the total
pressure applied through the pressure face.
However, within the constraints given, the curves
also can be used to identify tradeoffs in terms of the
cylinder diameter requirements at the hydraulic base
pressures given. To reduce the hydraulic cylinder
diameter, for example, an applied pressure of 2,000
psi can be achieved with two cylinders, each smaller
in diameter and each delivering the force of 1,000 psi
in applied pressure. Correspondingly, a single ram
delivering 3,000 psi of applied pressure can be
replaced by two or three rams totaling that pressure.
Also, the applied pressures can be generated by
one or more hydraulic pressure systems. For example,
3,000 psi of applied pressure can be provided by
three rams each giving 1,000 psi from one 5,000 psi
hydraulic system - or by two rams, one operating
with 5,000 psi of hydraulic pressure, the other with
3,000 psi.
In conclusion, the data in Figure 29 indicate that
a wide choice is available to press designers for the
execution of equipment performance specifications.
Since hydraulic cylinders of less than 30 inches in
diameter are commonly preferred for 3,000-psi
hydraulic systems, the data suggest a specification of
2,000 psi in applied pressure, some holding time, and
a bale volume not exceeding 0.75 cubic yard in the
compaction chamber.
Thus, the hydraulics information tends to
support the selection of presses made previously on
the basis of press capacity. Requests for bids on
hydraulic equipment in these general pressure ranges
should elicit a widespread response.
3. The Utilization of Hydraulic Forces
in the Compaction of Solid Wastes
The compaction curves in Chapter III of this
report indicate that initially a relatively small amount
of pressure is needed to achieve a significant volume
reduction of solid waste materials. About 80 percent
of the total volume reduction is achieved by about
1,000 psi which is half the total pressure applied at a
maximum face pressure of 2,000 psi. Similarly, 1,000
psi amounts to only one-third the ultimate pressure
applied if the maximum face pressure is 3,000 psi.
The approximate relationship is described again
in Figure 30, showing volume reduction and
461-084 O - 72 - 11
143
-------
0)
1 60
E
a
30
20
10
0.5 cubic yard compaction
chamber bale
Pressure area: 795 sq. in.
1.000 psi
hydraulic
pressure
2000 psi
hydraulic
pressure
3000 psi
hydraulic
pressure
5000 psi
hydraulic
pressure
0.75 cubic yard compaction
chamber bale
Pressure area: 1057 sq. in.
1000 psi
hydraulic
pressure
2DOO psi
hydraulic
pressure
3000 psi.
hydraulic
pressure
5000 psi
hydraulic
pressure
•v
Effect of pressure hold
1000 psi = 1750 psi
2000 psi = 2500 psi
at 3000 psi hydraulic
pressure
1000 2000 3000
* Basic data rounded in the calculation
1000
2000
3000
Applied Pressure (psi)
FIGURE 29
Interrelationship Between Diameter of Hydraulic Cylinder,
Hydraulic Pressure, and Pressure Applied for Two Sizes of
Bales in the Compaction Chamber*
144
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-o
E >-
— O
O i-
•M O
C
0) in
O 0)
J_ •—
-------
1. The Loading of the Press
The results of the previous discussions suggest
that solid waste compaction equipment might have to
operate at relatively high speeds. This makes it
essential for the press to be loaded in a minimum of
time.
Furthermore, compaction tests made during this
project, as well as previously by the APWA rail-haul
study team, indicate that the compaction of sets of
precompacted solid waste bales into one bale causes
severe laminations in the ultimate bale, even if
performed at very high pressures. Poor adhesion was
found at the interface of the precompacted portions
of the ultimate bale even when a final pressure of
18,000 psi was applied. In contrast, the compaction
of a full charge of wastes, not precompacted with
pressures exceeding those of a compactor truck,
produces no such lamination effects. Consequently,
the press loading facilities should be capable of
handling a full charge of uncompacted solid waste
materials.
In view of the nature and composition of solid
waste mixtures, it becomes apparent that any
forced-feed filling system may be highly complex and
costly. As noted earlier, such a system must be
capable of handling simultaneously an extremely
large variety of wet and dry materials ranging in size
from refrigerators and bedsprings down to tissue
papers and food scraps.
Thus, to provide for a fast and easy feed of the
input materials, the press should be designed for a top
or gravity-fill batch method of loading. Since
implementation of the press loading system is
considered part of the transfer station development,
it is discussed in the APWA rail-haul study.
2. The Charging Box
In terms of performance and design
specifications, it is necessary to determine the
dimensions of the charging box volumetric
requirements and the size of the opening. This finding
is based on the assumption that total volume
reduction is to be achieved by the press alone.
The data in Chapters II and III of this report
indicate that for handling of most normally delivered
residential wastes, the press would have to provide a
volume reduction ratio of 15:1. For a 0.50- or
0.75-cubic yard bale in the compaction chamber
press, this necessitates a charging box capacity of 7.5
or 11.25 cubic yards, respectively.
In a gravity-fill batch loading system, however, an
even filling of the charging box is not easily
guaranteed. Furthermore, oversized wastes such as
sofas or bedsprings might require an even larger
charging box; the above volume represents, therefore,
a minimum requirement.
The size of the charging box opening is
determined by the dimensions of the largest items
included in the material mix. Thus, in an ideal case
the cross sectional dimensions of the opening would
have to be sufficient to handle refrigerators, sofas,
tables, and freezers.
As a result, the dimensions of the charging box
might have to be increased by perhaps 50 percent
over the volumetric values given above. For example,
the side lengths of an 11.0-cubic yard charging box
would be only 2.2 yards, or 6.6 feet, if the box is
cube-shaped. This, in turn, would represent a pressure
face area of 43.5 square feet or 6,264 square inches.
For a 7.5-cubic yard charging box, the corresponding
side length dimensions would be approximately 1.9
yards or 5.7 feet, and the pressure face area would be
32.5 square feet or 4,680 square inches.
An increase of the side lengths of a cubic
charging box to about 10 feet would produce a
volume approximating 37 cubic yards. This would
correspond to a pressure face area of 100 square feet
or 14,400 square inches. If, in turn, 100 psi of
pressure were to be applied to this area, a total force
of 720 tons would be required.
In reviewing all the arguments presented thus far,
it becomes obvious that the application of a 720-ton
force to a 10 by 10-foot pressure face is technically
conceivable. However, an application of 2,000 psi, or
1 ton per square inch, appears to be needed for the
production of solid-waste rail-haul bales and would
require a force of 14,400 tons on the ram. Although
presses with such force applications are made, they
unfortunately are of relatively exotic design.
Thus, the implications of the charging box data
suggest development of a multi-stage compaction
press. Furthermore, attention must be given to the
data which indicate the presence of many voids in the
incoming refuse densities, and therefore, the small
forces needed for initial volume reduction. It appears
advantageous to give the cover of the charging box an
active function in the volume reduction process. This,
by itself, presupposes the use of at least a two-stage
compression system.
For example, the application of 10 psi over a 10
by 10-foot area would require a total force of 72
tons. Considering point loading, such a force is more
than adequate to crush oversized solid waste items
sufficiently to fit into a smaller charging box. Even a
force of only one-fifth that size, or 14.4 tons, and
representing a. pressure of 2 psi over the area, might
be all that is required. In view of the size of the total
146
-------
area, a significant portion of such a cover force could
be supplied by the weight of the cover itself.
Consequently, an active use of the charging box
cover in the compaction process can reduce the
pressure face area to which the second stage
compaction forces are applied. In addition, a
combination of the cover function with a compaction
function should be considered, since it would reduce
or eliminate a time element and therefore a cost
element that otherwise would have to be
incorporated in the over-all compaction operations.
In conclusion, the charging box analyses indicate
that the selection of a 0.50- or 0.75-cubic yard bale in
the compaction chamber press is reasonable for the
box dimensions required. With an inclusion of
oversized items in the solid waste mix, the charging
box dimensions appear to require the selection of
these bale-size specifications.
3. The Geometric Shape of the Compaction Chamber
For purposes of this project, the geometric shape
of the compaction chamber is derived from the
specifications for the bale form as outlined in Chapter
II. However, for non-rail-haul applications, other
shapes might prove desirable. Thus, to indicate other
applications of the project findings, it was found
necessary to consider other than rectangular shapes
for the compaction chamber.
In terms of press design, many geometrical shapes
of the compaction chamber are theoretically possible,
including cube, rectangular prism, hexagonal prism,
and cylindrical shape or ball. Some of these
configurations, such as a cube or a cylindrical shape,
lend themselves to a multi-stage compaction
approach. Others, such as a ball, might require the
compaction to be accomplished by a single stroke.
However, in considering various geometric shapes
of the bale and the compaction chamber, it is
important to take into account the nature of the
materials to be compacted. Certain geometrical
shapes such as a ball are impossible to make if the
input materials cannot be pre-processed to provide
sufficiently constant behavior patterns for the
materials under compaction. Consequently, certain
geometric shapes of compacted materials are possible
only in cases where the input materials are
homogeneous, as, for example, in the manufacture of
pills in the pharmaceutical industry. Thus, a
compaction of heterogeneous solid waste mixtures
into shapes such as a ball or a hexagonal prism should
not be attempted unless an adequate pre-treatment of
the materials is assured.
A brief survey of the applicable studies tends to
confirm this finding. It indicates that for the
compaction of heterogeneous materials such as metal
scrap or mixed papers, only cubical or rectangular
bale configurations are referenced. No other
geometric shapes appear to have been suggested for
use in standard practice.
In the light of these findings plus the test results
reported in Chapter HI and the conclusions drawn in
Chapter II, it was decided to confine the press
specifications to the production of square or
rectangular bales. Accordingly, the following analyses
of the compactor frame are based exclusively on
these shapes.
V. PRESS DESIGN CONSIDERATIONS
CONCERNING THE PRESS FRAME
The frame represents a large portion of the total
weight and cost of a compaction press. For metal
scrap balers operating at about 2,000 to 2,500 psi of
applied pressure, the frame often is estimated to
account for 40 to 45 percent of the total weight
and/or cost of the unit. Thus, since solid waste
disposal is highly sensitive to cost, it becomes
important to investigate some of the guidelines
governing the design of press frames.
1. The Press Frame in Terms
of Solid Waste Compaction
The frames used by relatively heavy presses
generally serve two basic functions. First, they carry
and/or contain, as a rule, the reaction forces resulting
from the application of pressure and/or impact.
Secondly, they provide, to varying degrees,
dimensional control for the compaction or fabricating
operations performed.
The second function, in particular, causes a
considerable over-design of the frame as compared to
the requirements for the first function. Specifically,
the frame in these cases frequently is designed on the
basis of stringent rigidity needs. These, in turn,
compel the main structural-frame members to operate
at a low percentage of their actual strength in order
to eliminate the deflections and elongations which
cannot be tolerated. As a result, press frames are very
heavy and have a high weight-to-force ratio for the
pressures actually applied in the compaction process.
In contrast, the dimensional variations of concern
for many fabrication and compaction processes are
not critical in the high pressure compaction of solid
wastes. Here some variation of the bale volume will
have to be accommodated in the compaction
chamber because of unavoidable variations in the
solid waste composition. Furthermore, the amount of
springback per individual bale after compaction is
both variable and substantial even at identical
compaction chamber dimensions.
Stringent dimensional control of the bale thus is
not possible, nor is it required for solid-waste
rail-haul. The ratio of frame weight to the amount of
147
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compaction pressure applied does not have to be as
high . as that normally found in compaction
equipment.
Solid waste compaction by hydraulic means
involves a relatively slow and gradual application of
the compression load without significant, or
continuous impact loadings. In turn, the absence of
dynamic loading in the form of impact can be taken
as added justification for development of
lighter-than-usual press frames.
Point loading can occur during the compaction of
solid waste mixtures. Although it is not likely to
cause damage to a lightweight frame suitable for the
pressures involved, the possibility of significant point
loading does exist. It appears that this fact, shown in
Figure 22, Chapter III, should be considered in the
design of a press and might deter the use of an
absolute minimum-weight press frame for solid-waste
compaction units.
Over-all, the above considerations encourage an
investigation of press frame design alternatives aimed
at construction of lighter frames than those found in
most existing compaction equipment. But while this
suggestion presupposes future improvements existing
frames are without doubt, technically suitable for the
construction of solid-waste presses.
2. Basic Considerations for a
Minimum-Weight Frame
The application potential of minimum-weight
frames to solid-waste presses merits further
investigation here, because of the importance of cost
reduction in solid waste disposal and the promise of.
solid-waste high-pressure compaction. In principle, all
the above arguments suggest that the design criteria
for a minimum-weight, s'olid-waste press frame might
be confined to the containment of the pressure
reaction forces excluding impact loading.
Within this context, it is essential to make the
total system reliable in terms of structural fatigue and
component wear. This requires that the frame
members be uniformly stressed in tension, preferably
by pre-stressing or, if necessary, by the compaction
process itself. For example, a frame design concept
could be used which would lesemble a pre-tensioned
wire rope system.
It is recognized, of course, that the frame for
solid-waste presses might not have to meet the
sophistication normally associated with such a
system. For example, welded plate or steel strapping
might be used as frame members to reduce structural
costs. Other alternatives, reminiscent of aerospace
minimum-weight — maximum-strength designs, might
be substituted for the massive side frame forgrugs and
tie rods commonly used.
The specific implications and execution of the
press frame design concepts touched on above are not
entirely new. Presses utilizing the underlying design
principles have been built in Europe. Furthermore,
the IIT Research Institute in Chicago uses a
lightweight frame made from steel strappings for the
end load restraint of a high-pressure chamber.
Thus, a distinct possibility exists for applying
minimum-weight press frame concepts in the design
of solid-waste high-pressure compactors. These
concepts may result in equipment of lower cost and
thereby increase the application potential of this solid
waste disposal process. They further justify the
continuation "of the investigation of lightweight
frames.
3. Description of an Existing
Single-Axis Lightweight Press Frame
As mentioned, IIT Research Institute has
developed, constructed and used successfully a
lightweight frame for a high-pressure chamber end
load restraint. It appears that an adaptation of the
IITRI concept could, for example, be used quite
Effectively for solid waste compaction presses.
However, IITRI's banded frame concept is not singled
out as the only realistic possibility for a lightweight,
low cost frame design. Rather, the HTRI approach
has been chosen as an example because it represents
the best documented system available within the
scope of this study.
Over-all, the IITRI strap-frame is capable of
carrying 9,000 psi of face or applied pressure for its
84-x-48-inch end section. This is equivalent to a force
of more than 18,000 tons on the ram. The face
pressure is at least four times as great as the face
pressures currently contemplated for the compaction
of solid-wastes.
The geometry of the IITRI press frame is
illustrated in Figure 31. It indicates the location of
the side and end frames and the direction of pressure
application. Specifically, it identifies the factors
which influence as discussed below the frame weight,
i.e., frame length, frame width, frame depth and the
loading applied.
In the IITRI press, the side or primary frame
members obey the criterion of minimum weight in
being required to carry only tensile stresses.
Furthermore, the side and end frame materials were
selected from the standpoint of minimum cost,
including both the material and fabrication
expenditures.
To satisfy the criteria of minimum weight and
cost for the primary frame, IITRI chose a 1022 steel
strapping with a cross section of 4.0 x 0.072 inches.
Thus, the frame is constructed of stacks of layered
148
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Direction of
Pressure
Application,
Location of
Hydraulic
Cyli nder
Location of End Frame
Side Frame
length-
End Frame
t
width
I
Direction of Force Application
FIGURE 31
Concept of the Geometry of the ITTRI Lightweight Press Frame
strapping to reach the total end load requirement of
approximately 36.3 million pounds or 18,150 tons.
Over-all, the IITR1 frame is designed to operate for
more than one million cycles at a tension stress of
35,000 psi.
It is important to recognize that a lightweight
frame within the context of this discussion is
composed of two distinct elements:
a) a high-tensile stress restraining system, and
b) a bearing plate system or end frame
progressively stressed by the increase in the
compaction pressures applied.
The end frame, according to IITRI, can be
designed to accommodate varying loads over the face
of the end plate. It could be made from one solid
plate, or from stacked solid plates which have the
advantage of low mill and fabrication cost. Point
loading might occur in the compaction of residential
and commercial solid wastes or their equivalents.
However, the compressive stresses in the end plates
are estimated in the order of magnitude of the
compaction pressures, provided the applied pressure
exceeds 2,000 psi.
4. Application of the Lightweight Frame
Concept to Multiple-Axis Compacting
The lightweight press frame concept appears to
lend itself to a multiple-axis compaction of solid
waste materials.
In solid waste compaction, a single-axis
compactor must have a very long tensile frame,
designed for the maximum compaction pressure,
because of the high volume reduction ratios. A
double-axis compactor, in contrast, requires a
shorter—perhaps very much shorter—tensile frame for
the containment of the peak compaction forces. In
double-axis compaction, the volume reduction is
accomplished by two rams, and it is commonly the
shorter of the two rams that applies the higher
compaction forces. Hence, compared to single-axis
compaction, the tensile or primary frames usually will
be lighter in double-axis compaction systems.
In principle, and with only a few exceptions, the
weight of the tensile frame decreases as additional
compaction stages are added to the system. This
results from an improved proportioning of the total
loading on the press frame, achieved by tailoring each
of the frames to contain only a portion of the total
pressures and ram travel distances involved.
•However, the actual tradeoff between the
addition of compaction stages and a decrease in the
weight of the tensile frame is governed, to a large
degree, by practical press operating and design
considerations. Too many individual frame elements
restrict the access to the press and might encumber
both the charging of the materials and the removal of
the bale. Furthermore, too great a dispersion of the
operating elements undoubtedly will complicate the
design' and construction of the press. It may also
increase, perhaps substantially, the total cost of the
individual press elements such as the hydraulic piping,
cylinders and controls.
In addition, end frames present some unique
problems. In contrast to the tensile frame paiameters,
the end frame requirements and weights always
149
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Pressure Face
Plate
Tensi1e Frame
FIGURE 32
Configuration of the Compaction Chamber
increase with the addition of compaction stages. A
double-axis compactor, for example, might require
two end frames. Both of these may be designed for an
equal amount of force, or one may be designed for
the peak compaction and the other for the lesser,
perhaps, greatly reduced pressure requirements.
Comparing a single-axis to a double-axis
compactor and assuming an identical size of the bale,
the end frame receiving the maximum forces is, in
both cases, capable of withstanding all the pressures
as applied through the whole pressure range. But
double-axis compression may require a second end
frame and therewith additional weight to stop the
forces applied in the first compaction stage. Thus,
while weight is, in most cases, taken from some
portions of the tensile frame by splitting the total
compaction process into separate stages, weight
appears always to be added by the same approach to
the end frame system. The total weight of the end
frames is almost always greater in multiple- than in
single-axis compaction systems.
In evaluating the application potential of the
lightweight frame concept to the design of solid waste
compactors, it must be remembered that (a) the
volume reduction ratio is substantially higher than
that usually found in other pressure application
processes, and (b) most of the volume reduction, in
terms of the ultimate force, is achieved by the
application of comparatively low pressures.
5. Effects of Compaction Chamber
Dimensions on the Press Frame
The geometry of the compaction chamber
influences the requirements for both the side or
tensile frame and the end frame.
The configuration of the compaction chamber,
referred to in the following discussions, is identified
in Figure 32. It should be emphasized that in these
discussions the length of the chamber is always
presumed to be parallel to the direction of the final
pressure application.
At a given amount of pressure, the end frame
requirements are determined only by the width and
depth of the compaction chamber. They are not
affected by changes in the length of the compaction
chamber unless the end frame area changes. For
example, at 2,000 psi of applied pressure and the
absence of pressure losses in the compaction, a
2-square foot end frame always would have to sustain
a 288-ton load, regardless of the length of the
compaction chamber.
On the other hand, the requirements for the side
or tensile frame are affected by changes in the width
and depth, as well as the length of the compaction
chamber. Changes in just the length of the
compaction chamber affect the design requirements
least. They require that the side frame be lengthened
or shortened, but they do not demand changes in its
capacity for end load restraint as long as the end
150
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frame area is kept constant.
However, changes in length of the compaction
chamber become highly significant to the side frame
requirements if a constant chamber volume is
postulated. In this case, the area of the end frame and
the length of the compaction chamber are
interdependent. An increase in the length of the
compaction chamber will decrease the end frame area
and vice versa. In turn, the end-load restraining
requirements, and therefore the tensile frame
requirements, may vary considerably.
An example of the interrelationship between
variations in the lengths of the compaction chamber
and corresponding end-load restraining requirements
is illustrated in Figure 33. The interrelationship is
shown on the basis of an 8-cubic-foot chamber
volume for applied pressures of 1,000, 2,000 and
3,000 psi.
An analysis of the three curves in Figure 33
indicates the same effects, regardless of the
1200
1000
o
it 800
•D
0)
L.
3
O"
(U
600
O)
c.
TO
400
200
100
1728 tons
864 tons
3000 psi applied pressure
"[OOO psi applied pressure
000 psi applied pressure
tons
288 tons
144 tons
12"
2V'
36" 48"
Length of Chamber (inches)
FIGURE 33
Selected Interrelationships Between Length of Compaction
Chamber and the End Load Restraining Forces Required for
a Chamber Volume of Eight Cubic Feet
151
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magnitude of pressure applied. Within the limits
given, a doubling of the length of the compaction
chamber reduces the end-load restraining
requirements by one-half.
The end frame load-bearing requirements will
change correspondingly in the case of a relatively
constant compaction chamber volume, which might
be required for the rail-haul of solid wastes. This is
illustrated in Table 52 for compaction chamber
length variations from 12 to 48 inches and a total
chamber volume of, again, 8 cubic feet.
corresponding hydraulics involved. The postulate of a
stable, cohesive bale requires that sufficient pressure
be transmitted throughout the solid waste mixtures
and, therefore, to the far end of the compaction
chamber.
6. The Operational Life of the Press Frame
The operational life of the press frame is
determined primarily by the applied number of cycles
of a given pressure or load.
A thorough analysis of this problem,
unfortunately, was outside the scope of this project.
TABLE 52
Variations in the Total End Frame Load Bearing Requirements Resulting
from Changes in the Length of the Compaction Chamber at a Load of 2000 psi
Applied to the End Frame and a Constant Chamber Volume
Compaction
Chamber
Vo 1 ume
(cu. in. )
13,824
13,824
13,824
13,824
13,824
13,824
Compaction Chamber
Dimensions
Length
(in.)
12
24
36
36
48
48
Width
Un.)
24
24
24
12
24
20
Depth
(in.)
48.0
24.0
16.0
32.0
12.0
14.4
End Frame
Dimensions
Width
(in.)
24
24
24
12
24
20
Depth
(in.)
48.0
24.0
16.0
32.0
12.0
14.4
Area
Isq.in.)
1152
576
384
384
288
288
Load Rqts.
at 2000 psi
Appl ied Press.
(tons)
1152
576
384
384
288
288
The data in Table 52 indicate the same
relationship for the end frame load-bearing
requirements as illustrated in Figure 33 for the
end-load restraining requirements. A doubling of the
length of the compaction chamber allows the
load-bearing requirements for the end frame also to
be reduced by one-half.
These findings are very significant in view of the
direct correlation between load carrying capacity and
material weight. The length of the compaction
chamber is identified in the foregoing analyses as a
prime factor governing the design of presses with
minimum-weight frames. In terms of the press frame
alone, the specifications for a solid waste compactor
should emphasize as long a chamber and bale as
possible.
For the total solid waste compaction process,
however, the long-length criterion calls for balance in
the relationship between (a) the pressure that has to
be applied (b) the pressures transmitted, and (c) the
It would require an investigation of the
interrelationships betweeji several variables and
tradeoff alternatives. Factors to be considered
include:
a) Over-all servi'ce-life requirements. For
example, is the press to last 5, 10, or 20
years and operate 5, 6 or 7 days per week
with 1, 2 or more shifts per day?
The number of cycles per minute.
The effects of various bale sizes. For
instance, the handling of 100 tons of waste
in 0.25-ton bales would require twice as
many cycles as the compaction of the same
tonnage into 0.50-ton bales
The characteristics and cost of the materials
that could be used in the construction of
suitable press frames, and
The advantages and disadvantages of using
more than one press for a given period of
service life.
b)
c)
d)
e)
152
-------
Accordingly, and because of the problem of
technological obsolescence, it was decided that cycle
life specifications for the rail-haul of solid wastes
should be calculated on the basis of:
a) A 10-year service-life
b) Six working days per week
c) A single 480 working minutes shift per day,
and
d) Two cycles per minute.
The calculations show that under these
conditions a press frame should be capable of
withstanding 10 x 6 x 480 x 2 or 2,995,200 cyclic
load applications. This is the equivalent of a 5-year,
2-shifts-per-day operation at the same number of
cycles per minute, and a 20-year, 1-shift-per-day
operation at 1 cycle per minute.
Most installations should be well served by these
cycle specifications. Installations, required to operate
at a high level of production are more likely to gain
from technological progress, such as improvements in
press design than those facing less severe throughput
demands. Furthermore, kinds of materials suitable for
the press frame might make a 3-million cycle
requirement equivalent to an unlimited service life in
certain instances.
Evaluation of the total cycle implications must
recognize again that the hydraulic compaction of
solid wastes, as dealt with in this project, is not
carried out by impact. The process, although fast
perhaps in certain sub-operations, applies the pressure
gradually and continuously throughout the total
pressure range. In addition, the elasticity and high
compressibility of the solid waste mixtures cause
some cushioning in the load application. However, as
indicated in Chapter III, II-6, appreciable peak forces
nevertheless, can be developed, and these stresses
must be considered in implementing the above cycle
specifications.
VI. CONSIDERATIONS ON PRESS
FOUNDATIONS
The foundation requirements for a compaction
press are very important since they may constitute a
controlling cost factor in the selection of a
compaction site. Thus, the foundation requirements
should be considered in the design of the compactor
itself.
Within the scope of this project, it was not
feasible to investigate the implications of press design
alternatives in terms of self-contained or
not-self-contained compaction units. A self-contained
unit is defined as a press which does not require
structures other than those provided by the press
itself for the containment of the forces developed
during the compression process.
The wide variety of both local conditions and
press alternatives suggest that the design and
manufacture of self-contained presses might be less
complicated than the implementation of
not-self-contained presses. Therefore, it was decided
to base the consideration of press foundations
exclusively on factors associated with self-contained
compaction units. The foundation requirements for
these must embrace primarily the load to be carried,
the shape or configuration needed, and cost. The
governing factors, in turn, include the weight of the
machine, the floor area requirements and the soil
conditions.
The loading on the foundation is determined
almost totally by the weight of the compaction unit.
It should be recalled in this context that th%
hydraulic compaction of solid wastes is relatively
slow and involves materials of relatively low stiffness.
Thus continuous and/or major dynamic impacts are
not likely to occur.
Furthermore, a single or multiple-axis compactor
can be designed in such a way that all force
applications take place in a horizontal plane. This will
result in a relatively large foundation area, with,
however, a relatively low area loading. The horizontal
positioning of the axes of compaction eliminates the
need for a pit or a complex shape of the foundation.
In contrast, compactors using a vertical
arrangement of one compaction stage need a smaller
foundation area. However, they do require perhaps a
more complex foundation to support more of the
total weight of the press on the smaller area. This, in
turn, usually necessitates foundation reinforcements.
Unfortunately, reinforcements for concrete, such as
placed steel wire and bar reinforcements, are very
expensive. Furthermore, the costs of foundation
forms vary greatly, depending on soil conditions and
the complexity of the foundation shape.
The specific foundation design for a compactor
will, of course, require a detailed analysis for each
specific se* of parameters. The general arguments
made above -permit conclusions adequate for the first
phase of the APWA rail-haul project but not
sufficient for the implementation of demonstration
projects.
In general, the foundation analyses suggest that
solid waste compaction should preferably take place
in the horizontal plane. If a choice has to be made
between (a) land acquisition opportunities and/or
cost and (b) foundation cost, the press should be
designed to avoid the construction of a pit. This, in
153
-------
turn, suggests that if compaction is to take place in
the vertical plane, the compression forces should be
applied from above.
SECTION TWO-SELECTED COMPACTION
EQUIPMENT PERFORMANCE SPECIFICATIONS
The term "performance", as used in this section,
refers to the functions the compaction unit has to
complete to produce bales suitable for rail-haul. It
does not address itself to the specific elements of
press design needed to execute the compaction
functions.
The information in this report provides a variety
of inputs for establishment of compaction equipment
performance specifications, and suggests that
ultimately several sets of specifications may be
developed.
Variables in local conditions have been identified
as significant factors in drafting appropriate
specifications. Selection of process, capabilities must
mesh with the local solid waste disposal objectives,
input materials, and the chosen type of operations.
Within the scope of this project a framework
could not be developed for even the major
specification series possible. Nor was it feasible to
develop more than one highly general specification
example. It is suggested that additional specification
work be done in the context of demonstration
project developments, which are scheduled for the
second phase of the APWA rail-haul study.
After evaluation of the data already discussed, it
was decided to draft the specification example for a
press producing a bale of about 0.50 cubic yard in the
compaction chamber. Covering only the functional
compaction performance requirements of the press
unit in general, this example covers:
Materials to be compacted:
heterogeneous mixtures of solid waste materials
which behave like semi-elastics under
compaction.
Press loading:
by fast gravity-fill 'batch system, delivering the
input charge in less than 5 seconds.
Volume Reduction ratio:
18:1
Pressure applied during final compaction stage:
2,000 psi
Pressure hold time:
15 seconds at 2,000 psi
Total cycle time:
1 minute
Service life:
total number of cycles—2.9 million.
Bale volume in the compaction chamber:
13 to 16 cubic feet, average 14 cubic feet.
Weight of bale in the compaction chamber:
as a rule, between 1,200 and 1,400 pounds
Dimensions of bale in the compaction chamber:
25.7 x 27.7 x an average of 34.0 inches and
slightly variable.
Direction of pressure application for multi-stage
presses in reference to bale dimensions in the
compaction chamber:
Double-axis press:
25.7 inches = fixed
27.7 inches = parallel to direction of pressure
application by 1st ram.
34.0 inches = parallel to direction of pressure
application by 2nd ram (final pressure
application)
Triple-axis press:
25.7 inches = parallel to direction of pressure
application by 1st ram
27.7 inches = parallel to direction of pressure
application by 2nd ram
34.0 inches = parallel to direction of pressure
application by 3rd ram.
Special provisions.
locks needed to keep the rams not applying the
final pressure in their fully extended position
during the final pressure application, including
any pressure hold time.
The dimensions for the compaction chamber
were derived by combining the bale size postulates
identified in Chapter II of this report with the
findings on springback presented in Chapter III.
Springback in the direction of the final pressure
application averages about 50 percent. Thus, the bale
dimension pegged at about 34.0 inches in the
compaction chamber will grow to about 51.0 inches
after springback.
For this press specification, it was assumed that
the bales would be loaded in the rail car two rows in
height and that bale height would refer to the bale
dimension parallel to the direction of the final
pressure application. As a result, the total height of
the lading in the rail car would average about 102
inches, which complies with loading height limitation
of 108 inches.
Springback, in respect to the other dimensions, as
shown in Chapter III, always was found to be least in
the direction of the lowest pressure application. It
154
-------
amounted, in the experiments, to about 5 percent for
the first ram pressure application, and 10 percent for
the second. Thus, the 25.7 inch compaction chamber
bale dimension would grow to about 27 inches, after
springback, if a similar configuration for the press and
the pressure application were used. This is the
equivalent of the 2.25-foot bale side identified in
Chapter II among the alternatives suitable for the
width of the rail car.
As a result, this sample specification assumes that
the bales would be loaded four in a row to fill the
width of the car, which is about 9 feet. The first
compaction chamber dimension was selected to
correspond to the 2.25-foot bale dimension, because
the amount of springback was always found to be
least, and also vary the least, in the direction parallel
to the lowest pressure application.
Thus, least amount of variation in the directional
orientation of the springback is matched to the
dimension in the bale loading configuration which, as
outlined in Chapter II, is critical as applied to both
rail car design and lading.
In addition, the press specifications as given in
this example can be used to determine the length of a
solid waste rail car. An average springback of 10
percent in the remaining 27.7-inches bale compaction
chamber dimension would result in a bale dimension
of about 30 inches. Since eight bales, stacked as
stated above and weighing about 1,300 pounds each,
would have a total weight of 5.2 tons, it would take
19 to 20 rows of bales to make up a load of 100 tons.
In turn, the loading space in the rail car would have
to be about 600 inches (20 bales x 30 inches each) or
about 50.8 feet long.
The specification of 2,000 psi of applied pressure
and a 15-second pressure hold was chosen for several
reasons. First, compaction with 2,000 psi of applied
pressure appears, as shown in Chapter HI, sufficient
to produce stable bales for the compaction chamber
size given. Second, the addition of the 15-second
pressure hold at 2,000 psi can produce bale
characteristics equivalent to those achieved at about
2,500 psi of applied pressure without a pressure hold.
Thus, the 15-second pressure hold will provide an
added margin of safety in achieving the compaction
objectives.
Third, the tests suggest that compaction of solid
waste mixtures with an appreciable amount of
moisture is better at 2,000 psi than at higher pressure
application, and retains more moisture. The
possibility of moisture and pulp blowoffs under these
conditions is also reduced.
Over-all, the press specifications appear well
suited to the solid waste rail-haul requirements
outlined in Chapter II. It is hoped that all the data
will encourage press manufacturers to establish
additional specifications and develop widely
applicable solid waste compaction equipment.
SECTION THREE-PRICES AND CONSTRUCTION
COST ESTIMATES FOR HYDRAULIC PRESSES
POTENTIALLY SUITABLE FOR THE HIGH
PRESSURE COMPACTION OF SOLID WASTES
Solid waste disposal, as pointed out in Chapter II,
is highly sensitive to costs. Moreover, a high pressure
solid waste compaction process will have to compete
with many alternate methods of disposal.
A striking relationship seems to exist between the
number of potential process installations and the
amount of the unit price. In broad terms, a decrease
in the press unit price causes a disproportionate
increase in the total press sales volume. The smaller
the community, governmental jurisdiction, or transfer
station service area, the greater is the importance of
low equipment price.
It should be stressed that governmental
jurisdictions are more often medium-sized or small,
even if located in a metropolitan area.
1. DATA LIMITATIONS
The information offered here can present only an
approximate estimate of press prices and construction
costs. More precise information was not readily
available, nor did it come within the limitations of
this project. A myriad of factors, interrelationships
and tradeoffs must be considered in applying value
engineering techniques to press design and
construction.
All the following information is based on quotes
and cost studies accessible to the project team.
Although most of this is classified as preliminary in
nature, it is considered reasonably accurate by those
who supplied it.
The estimates are confined to hydraulic presses.
Since these presses are expected to be the primary
element in the first generation of solid waste
compaction equipment, their prices may serve as a
reasonable indicator in comparing the economics of
competitive processing methods.
The data present the direct investment cost or
straight purchase price as well as the energy cost.
They do not include the cost for the foundations,
transport of the press to the site of operations, and
installation, nor any personnel, maintenance or
supply expenditures.
The information can serve as a broad guideline
to:
a) assist decision-makers in government and
155
-------
industry in the initial planning for the rail-haul of
solid wastes, and
b) help in allocating responsibilities for preparation
and implementation of bid specifications which
always are costly and time consuming for both
government and industry.
II. PRICES AND COST OF EXISTING
HYDRAULIC PRESSES
Some guidelines on prices and costs can be
established for this analysis by an investigation of
presses already on the market and roughly suitable
for the compaction of solid wastes.
Certain of the data obtained in this investigation
are summarized in Table 53 on the following page.
The press examples given include entries from most
of the major metal scrap baler manufacturers.
It must be stressed in the presentation that with
the exception of entry "F," none of the presses
originally was designed for the compaction of solid
wastes. Only entry "F" gives data from a firm
proposal for the sale of a solid waste compaction
press. However, all the other presses could be used for
compaction if necessary.
Significantly, none of the presses, including entry
"F," would be designed as is for such compaction.
For example, the volume reduction ratio of the press
in entry "F" is substantially too low if a bale of 2.0
cubic yards is to be produced, while the volume
reduction ratios for entries "A" to "E" sometimes are
substantially too high for the bale sizes indicated.
Some of the pressures are too low for the size of the
bale, excluding holding time, while others are too
high.
Furthermore, the power costs quoted are judged
to be high. The full power is used, as a rule, only
during a relatively short portion of the compaction
cycle. For a given period of time, the actual power
consumption is frequently calculated to be 35 to 40
percent of the total horsepower installed. However, in
the absence of (a) any detailed backup data on the
actual power consumption, and (b) specific
investigations to gauge the time-power needs of the
compaction, it appeared advisable to use a higher
power demand factor.
Despite these critical comments, the data in
Table 53 suggest that the high pressure compaction of
solid waste promises extremely attractive economics
as well as basic performance capabilities. Assuming a
properly designed press, the data support the APWA
rail-haul interim report in estimating that compaction
may cost less than 40 cents a ton, including
depreciation, maintenance and power.
HI. COST ESTIMATES FOR A LIGHTWEIGHT
FRAME SOLID WASTE COMPACTION PRESS
The following cost estimates for a lightweight
frame, solid waste compaction press are based on
HTRI experience in the design and construction of its
large, high pressure evaluation vessel. The relatively
well-documented IITRI costs were used to help
project solid waste compactor costs in terms of
different bale sizes in the compaction chamber.
Thus the cost estimates given represent the
experience of only one approach to the design and
construction of a lightweight press frame. Other
approaches obviously are possible and most likely will
result in different cost estimates.
As mentioned before, the IITRI approach was
chosen for this analysis because it represents the best
documented examples available within the constraints
of this study.
As pointed out previously, the engineering of a
press is estimated to take as much as 3,000 to 4,000
manhours. More time obviously would be required
for the development of a new prototype press, since
many variables and tradeoff alternatives must be
established and evaluated carefully.
Over-all, the cost estimates presented might be
considered the approximate minimum for presses of
the same compaction chamber bale dimensions. It
might be recalled that the HTRI design, although
incorporating a safety factor of 2.0 to 2.5, has an
attractively low weight-to-force ratio for its frame
structure. This is significant since press frames may
account for as much as 40 percent of the total weight
of existing presses potentially suitable for the
compaction of solid wastes.
The estimates were made for single- and
double-axis compactors and various sizes of cubic
bales ranging from 0.3 to 1.0 cubic yard in the
compaction chamber. It was discreetly assumed that a
final pressure of 3,500 psi would be applied to the
bale and that a volume reduction ratio of 18:1 would
be required. Finally, the frame weight calculations
were made to differentiate between standard and
lightweight end frame sections as evolved from the
IITRI experience.
Based on the IITRI strap frame design and
construction experience and the specific materials
used, the calculated frameweights are shown in Table
54.
156
-------
TABLE S3
Summary of Economic Data on Hydraulic Presses Potentially Suitable
for the Compaction of Solid Wastes
Press Specifications
and Evaluation Parameters
DESCRIPTION OF PRESS
Charging Box Dimensions
a) Configuration (inches)
b) Cubic Feet (number)
c) Cubic Yard (number)
Bale Dimensions
a) Configuration (inches)
b) Cubic Feet (number)
c) Cubic Yard (number)
Theoretical Volume Reduction Potential
In Terms of Press Dimensions as Given
by Sizes of Charging Box and Bale
(ratio)
Compaction Process
a) Number of compaction stages
b) Pressure applied to materials
ba) first stage (ps i )
bb) second stage (psi)
be) third stage (psi)
c) Total force applied on the ram
in the final compaction stage (tons)
d) Operating time and production
da) cycle time (minutes)
db) bales per hour (number)
dc) provision for pressure
hold ing t ime
Hydraulic Parameters
a) Capacity of Pumps (gpm)
b) Size of fluid reservoir (gallons)
c) Power supply
ca) type
cb) capacity (hp)
Overall Press Dimensions
a) Configuration of floor area (feet)
b) Shipping weight (pounds)
c) Plane of operations
Purchase Price F.O.B. Factory (dollars)
SELECTED PRESS COMPARISON AND
EVALUATION DATA
1. Production of solid waste bales based
on a material density in the compaction
chamber of
a) 90 Ibs/cuft at 2000 plus psi
applied pressure, (tons/hr)
b) and 80 Ibs/cuft at 1000 to
1500 psi applied pressure (tons/hr)
2. Price per pound of shipping
weight (dollars)
3. Price per ton of hourly
production (dollars)
4. Price per ton at 18,200 hours
of production (dollars)
[7 hrs/day, 5days/wk, 52wks/yr,10 yrs]
5. Price per ton at 36,400 hours
of production [20 yrs] (dollars)
6, Price per horse power (dollars)
7- Power cost per hour at a 60$
utilization of the installed
horsepower capacity and 1-1/2
Hydraulic Press Examples
A
24x48x96
64
2.37
! Ax 14x22
2.49
0.09
26:1
2
262
1475
-
227
2.4
25
none
216
575
electric
motor
75
23x23
75,000
hor i zontal
40,000
-
2.49
0.53
16,064
0.88
0.44
533
cents per kilowatt hour (dollars)1 0.50
8. Power cost per ton of hourly
production (dollars)1 0.20
9. Total direct compaction process (dol lars/
cost, 20-year service life ton)
0.64
B
37x58x150
186
6.88
24x16x35
7.77
0.29
24:1
2
272
1620
-
452
3.0
20
none
432
1200
electric
motor
150
31x26
176,000
horizontal
84,000
C
48x72x144
288
10.66
24x22x48
14.66
0.54
20:1
2
233
1350
-
716
2.5
24
none
752
4000
electric
motor
400
38x32
280,000
hor i zontal
165,000
i
-
6.22
0.4?
13,505
0.74
0.37
559
1.00
0.16
0.53
-
14.07
0.59
11,727
0.64
0.32
413
2.68
0. 19
0.51
D
40x50x1 16
134
4.96
14x14x24
1.58
0.06
82: 1
3
95
685
2450
240
0.6
100
none
325
N.A.
electric
motor
210
30x27
100,000
lorizontal
93,500
7-11
-
0.93
13,150
0.72
0.36
445
1.41
0.20
0.56
E
60x80x280
777
28.77
24x24x24
8.00
0.30
96:1
3
106
735
2460
707
1.5
40
none
565
N.A.
electric
motor*
410
27x59
465,000
horizontal
265,000 .
14.40
-
0.57
18,403
1.01
0.51
645
2.75
0. 19
0.70
F
51x90x168
446
16.52
36x36x72
54.00
2.00
8:1
2
740
2180
-
1700
1 .6
36
none
N.A.
N.A.
electric
motor
500
26x43
390,000
lor i zontal
300,000
87.48
-
0.77
3,430
0.19
0.10
600
3-36
0.04
0.14
157
-------
The data given in Table 54 show that a
replacement of the standard end sections by
lightweight end sections reduces the total frame
weight by 22 to 26 percent. The data also indicate
that the addition of a second compaction stage
reduces the frame weight by 36 to 42 percent as
compared to a single-axis compaction press.
The frame weights given in the above table were
used for the press cost estimates by employing the
following relationship-
CT = £WWT
wf
where
Op = the total cost of the press
C\y = the cost per pound of material
Wj = the total weight of the frame, and
Wf = the fraction of the total frame weight in
terms of the total weight of the press.
In gauging the estimate patterns, it was assumed
that the fraction of frame weight to total press weight
would vary from 25 to 40 percent. The basis was that
the weight of the frame itself would decrease while
the weight of the hydraulics and other press
components would remain constant.
In addition, two prices per pound of
material-Si.00 and 75 cents-were introduced into
the calculations. This selection is based on data
established earlier for existing compaction presses.
Thus, the estimates reflect the cost experience with
presses produced in quantities greater than one. The
cost undoubtedly will be higher for a prototype press,
if the expenditures for the conceptual design,
engineering and any special tooling are included.
The end results of all the calculations are
summarized in Table 55 on the following page. Here
are examples of how the development of a
lightweight frame, hydraulic solid waste compactor
might promise extremely attractive investment
economies. For example, at an over-all material cost
of $1.00 per pound, a 0.6-cubic yard bale in the
compaction chamber, a standard end section, and a
frame weight representing only 25 percent of the
total press weight, a double-axis lightweight frame
compactor might cost approximately $104,000. This
is, within the context of this study, the tentative
order of magnitude if a cost/price indicator is to be
eiven
To place these cost estimates into perspective, it
must be recognized that for a 20-year useful service
life the direct depreciation cost for this compactor
amounts to $5,200 a year. At a production rate of
just 1 bale per minute, an average density of 1 ton per
cubic yard in the compaction chamber and an
effective production time of 7 hours per day for only
5 days per week and 52- weeks per year, this
compactor would process 7 x 60 x 5 x 52 x 0.6, or
65,520 tons of solid wastes per year. Thus, excluding
interest cost and return on investment, the direct
depreciation charges for the press would amount to
only $0.079 per ton.
TABLE 54
Estimated Lightweight Frame Weights for Single- and Double-Axis
Solid Waste Compactors, Based on Different Bale Sizes, Two Types of End
Section Construction, a Cubic Configuution of the Bale in the Compaction
Chamber, and an 18'1 Volume Reduction Ratio.
Type of Compactor
Single -Ax i s
Double-Axis
Bale Size
(cubic yards)
0.3
0.6
1 .0
0.3
0.6
1.0
Total Frame Weight*
Standard
End Sections
(tons)
11.1
21. A
38.5
7-1
13.0
22.2
Lightweight
End Sections
(tons)
8.2
18.0
30.0
5.k
10.7
17.3
Source: IIT Research Institute
* Data slightly rounded
158
-------
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The data presented in Table 55 lend themselves
to numerous cost/performance calculations of the
type just described. Combined with other data given
in this section and other parts of the report these cost
estimates indicate that high pressure compaction of
solid wastes is feasible. This is particularly true if
lightweight frame press designs are utilized since they
have substantial advantage both in terms of
investment and operating cost.
SECTION FOUR-IMPLICATIONS OF THE
HIGH PRESSURE COMPACTION OF SOLID
WASTES WITH RESPECT TO RAIL-HAUL
In the rail-haul of solid wastes, the use of high
pressure compaction must be viewed in terms of the
three major system building blocks. As indicated in
the APWA rail-haul interim report, these building
blocks are (1) the transfer stations, (2) the rail
transport link, and (3) the sanitary landfills. Also as
indicated in that report, public health and
environmental control are of substantial
consideration in each of these building blocks as well
as the system as a whole.
Since a detailed discussion of the implications is
planned for the final report on that rail-haul study,
the concern here is with rail-haul development
benchmarks rather than specific parameters for the
equipment and operations.
Generally, this report should provide sufficient
information to gauge the influence of variables
critical to applying high pressure compaction to
solid-waste rail-haul. However, this project permits
the major variables to be outlined only in an
indicative rather than definitive way.
I. OVER-ALL PUBLIC HEALTH AND
ENVIRONMENTAL CONTROL ASPECTS
The combination of high pressure compaction
and rail-haul tends to reduce the pollution burden to
the environment, as contrasted to other commonly
used solid waste disposal process, especially in the
absence of pollution controls. Moreover, the
compaction process and rail-haul require a lesser
quantity and sophistication of pollution control
equipment than some of the other waste disposal
processes.
Finally, there is substantial indication that the
high pressure compaction process itself not only
avoids causing pollution but can be developed
through further research into a valuable tool for
environmental control.
H. THE IMPLICATIONS WITH
RESPECT TO TRANSFER STATIONS
The implications covering transfer stations for
the rail-haul of solid wastes can be summarized
briefly as follows:
1. Foundations
The utilization of high pressure compaction
equipment will not, as a rule, necessitate the
construction of a pit under the press.
A press may weigh from about 50 to 150 tons
and require a maximum floor area of about 1,300
square feet.
The specific foundation requirements, as
indicated previously, will have to be worked out in
terms of a given installation or demonstration project.
2. Pretreatment of the Solid Waste
Input Materials
As a rule, residential, commercial and general
industrial solid waste materials as collected by
normal, properly operated collection systems, can be
compacted and baled successfully. No pre-treatment
of the input materials is required in such cases.
However, as indicated in Chapter III rubber tires
must be excluded unless they are shredded and
reduced to small pieces of perhaps 1 to 2 cubic
inches.
Implications must be considered for route
layouts in certain collection systems, such as
exclusive service of commercial districts and suburban
residential settlements. Care must be taken to prevent
certain components from representing too large a
portion of the mixture making up an input charge.
This applies especially to vegetable or garden type
wastes and dirt.
Furthermore, solid wastes heavily wetted by rain
cannot be compacted into a stable bale without the
use of aids producing the required stability. But
generally a light mixing of the solid waste materials
prior to charging the press may be all that is needed
for adequate preparation of the solid waste input.
The conditions existing at a given transfer station
will, of course, determine both the pre-treatment
method and the amount of any necessary
pre-treatment. Preliminary investigations made for
the APWA rail-haul project suggest that inexpensive
methods already are available and appear to be
adequate.
3. Press Loading Equipment
The amount of solid waste material input
normally is to be controlled by weight only. This is
one of the major findings of this project, which has
proven that input control by volume is detrimental to
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a rational process design and that a weight/volume
input control is unnecessary.
For high throughput operations, the press loading
equipment should be capable of charging the press by
a gravity-fill batch system with about 1,400 pounds
of solid waste materials in less than 5 seconds, once
every minute.
The performance requirements are less
demanding for transfer stations handling fewer than
250 tons per shift.
To correspond to the press specifications for a
given transfer station, the press loading equipment
will have to be determined ultimately in terms of a
demonstration project.
4. Handling of the Bales
Almost all of the existing material handling
methods are well suited to the transport of bales in
the transfer station, the movement to and from any
storage area, and the loading of the rail cars.
However, a slight amount of material spillage will
occur, particularly if the bales are made from refuse
charged into the press in a loose state and not
contained in paper sacks. The findings of this project
suggest that the spillage from bales of loose wastes
amounts to less than 1 percent of the total weight of
the materials processed. An inclusion of oversized
metallic solid waste items in the input mix, or use of
paper sacks in the collection system, will reduce this
percentage substantially.
5. Storage of Bales
The bales are suitable for any length of storage
that might be contemplated within the context of
currently envisioned rail-haul systems.
The specific height of the bale storage must be
gauged to the rail car loading configuration. The
findings of this project indicate that bales can be
stored at least 8 to 10 feet high without any load
carrying supports.
Provisions should be made for ventilation of the
storage area. However, high capacity ventilation
equipment is not required. A slight natural draft,
obtainable through proper design of the building,
apparently is sufficient.
6. Public Health and Environmental Control
To assure proper industrial hygiene and working
conditions, the transfer station area housing the
compaction process must be provided with active
ventilation to be used as needed.
In addition, the area around the charging box and
the compaction chamber of the press requires a
drainage system and treatment for the runoff of any
leachants. This system should be capable of handling,
on the average, a maximum of 2 quarts of runoff per
ton of materials processed.
The parts of the press and transfer station in
contact with the solid waste materials and
particularly the leachants must be cleaned at regular
intervals.
7. Cost
In terms of the press only, it will cost an average
of 40 to 50 cents to compact 1 torn of solid waste
materials. These figures exclude finance charges such
as interest foundations and labor, to allow for local
conditions and arrangements. In some instances the
press may operate automatically; in others a press
operator may be required. The total owning and
operating cost for a compaction process-transfer
station will be developed in the final report of the
first phase of the APWA rail-haul study.
III. THE IMPLICATIONS WITH RESPECT
TO RAIL TRANSPORT
The implications for rail transport in terms of rail
car design; the bale loading configurations, and the
direct rail transport are summarized as follows:
1. Bale Loading Configurations
It is possible to design many configurations for
the loading of bales on a rail car. In terms of the
bales, almost any loading configuration can be
implemented successfully.
As a result, the specific bale loading
configuration can be determined almost entirely in
terms of the rail-haul system operations developed for
a demonstration project, including the selection of
rail cars and loading equipment.
2. Rafl Car Design
The rail car should be covered primarily for
reasons of public relations, but also for reasons of
environmental control. As shown in Chapter IV,
exposure to the elements apparently has no
appreciable effect on the stability characteristics of
the bales. However, in cases of rain, the accumulation
of wafer in the rail car might be disadvantageous.
Also an open car, especially if it has to stand in a
station for long during warm weather, may attract
flies or other insects.
The rail car should be designed to facilitate the
loading and unloading of the bales in sets. Thus, an
all-door boxcar appears to be most suitable for the
rail-haul of solid wastes.
In addition, the car design must "be integrated
with the material handling methods chosen, or vice
versa. For example, the car floor might have to be
grooved to permit the loading and unloading of bale
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sets by heavy industrial fork-lift trucks.
It would be advantageous for the car to have
movable bulkheads to assure a tight fitting load, as
variations in the bale dimensions occur. In all door
cars these movable bulkheads preferably might be
placed in the center to achieve maximum effect and
enhance the cost-performance ratios as applied to the
car structure.
Also, the doors might be hinged to provide about
1 inch of additional clearance for their " move"
position as compared to their "closed and locked"
position. Thus, if the bales should shift or expand
during transport, any possible jamming caused by
friction between the bale surfaces and the door would
be avoided when the doors are opened.
The stability experiments suggest that solid waste
rail cars do not need more than the normally required
spring systems to cushion the lading against vibration
and shock.
Ventilation of the car would be beneficial.
However, force ventilation devices are not required. A
simple circulation of outside air through the car is
sufficient, particularly if the amount of air admitted
and exhausted can be controlled in accordance with
seasonal temperature changes.
3. Transport Operations, Distance and Routing
All railroad operations, as commonly performed
today, are well suited to the shipment of solid waste
bales. These include the switching, classification, train
assembly, and over-the-road travel.
Compacted solid waste bales can be' shipped for
long distances. Thus interstate solid waste rail-haul
networks can be set up where necessary or desirable.
Routing alternatives and condition of infrequently
used tracks do not appear to be significant
Considerations in the selection of a specific transport
configuration.
Thus, solid-waste rail-haul networks can be
designed exclusively on the basis of maximum
efficiency for the movements involved.
IV THE IMPLICATIONS WITH RESPECT
TO SANITARY LANDFILLS
The implications of placing solid waste bales
compacted at high pressures in sanitary landfills are
viewed in reference to the construction and operation
of the landfill as well as the on-site environmental
control measures.
1. The Basic Construction of Sanitary
Landfills for the Disposal of
Solid Waste Bales
Placement of highly compacted solid waste bales
int'o sanitary landfills requires basic landfill
construction specifications of the same order as those
for unbaled and/or less compacted refuse.
Provisions for the escape of gases might have to
be made. Drainage installations required for the
removal of leachants or seepage need not have the
same capacity as those required for ordinary landfills
of comparable size, since highly compacted solid
waste bales resist water percolation more than less
compacted wastes. Provisions for rain water runoff
must, of course, be made and should follow the
normal landfill experience in a given location.
Generally, the specific landfill construction will
have to be determined in terms of a given case or
demonstration project, and some significant tradeoff
alternatives must be considered. For example, the
requirements for roads in the landfill depend upon
factors such as the weight of the bale loads
transported, the total volume of wastes disposed of,
the landfill depth, the location of the railroad siding,
the method of on-site bale transport, the soil
conditions, and the availability of cover material.
In evaluating the basic construction implications,
it should be recognized that highly compacted solid
waste bales allow for a much better use of available
landfill space than is common with current methods.
Solid waste bales permit an increase in the space
utilization by about 60 to 90 percent, since they
could average from 1,600 to 1,900 pounds per cubic
yard as compared to a maximum density of about
1,000 pounds in most of the existing landfills where
loose refuse is buried.
2. Operations of Landfills for
Solid Waste Bales
The operations landfills for solid waste bales
differ in several respects from existing landfill
operations.
First, solid waste bales do not require on-site
compaction. Second, the bales must be transported
from the rail head to the actual disposal spot. Third,
fullest use of the available space calls for a placement
of the bales by stacking or an equivalent method.
The establishment of detailed cpst-performance
parameters requires, of course, both the specification
and analysis of the needed equipment
implementation. Examples of such an evaluation are
given in the first phase report of the APWA rail-haul
study.
3. Public Health and Environmental
Control Measures
In terms of environmental control, solid waste
bale landfills appear to have distinct advantages over
existing landfills.
First, there is much less chance for papers to be
blown around in high winds. Second, solid waste
bales do not burn as easily as uncompacted waste
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materials. Third, should smoldering fires occur in a
bale fill, they possibly would not be as severe as those
in existing landfills because the presence of oxygen is
reduced. And fourth, there is less chance for odors to
escape, since less of the material is exposed to surface
winds than in landfills handling uncompacted wastes.
Over-all, the utilization of high pressure
compaction as an integral part of sanitary landfilling
offers the promise of climating many complaints
stemming from lack of environmental control. Less
emphasis has to be given to the care with which the
operations are performed. In the high pressure solid
waste compaction processes, most of the significant
environmental control measures are built in
automatically and not subject to human error or
negligence.
V. CONCLUSIONS
Implications of high pressure compaction for the
rail-haul of solid wastes could be evaluated and
discussed only briefly within the scope of the present
project.
The information strongly suggests not only that
major difficulties can be avoided, but that substantial
benefits can be gained.
It should be repeated that (a) selected details of
the implementation are given in the report on the
first phase of the APWA rail-haul project and (b)
because of the numerous interrelationships and
variables involved, the specifics can be quantified 01
judged only by actual cases and/or a demonstration
project.
SECTION FIVE-OUTLOOK
The present project has demonstrated that the
high pressure compaction of solid wastes may be
ranked among the most attractive of solid waste
disposal processes.
The results of this project suggest that additional
testing and development might lead quickly and
efficiently to substantial improvements. These
investigations will reduce the lead time required to
implement the installation of high pressure
compaction systems.
Further process improvements must recognize
that solid waste disposal represents a more complex
system than is commonly supposed. The
interrelationships among the manifold material,
equipment and operation factors seem to demand a
comprehensive, well integrated pattern of research.
Specifically, the project findings suggest followup
research on:
a) Development of a lightweight press
tailor-made for the high pressure compaction
of solid wastes.
b) Behavior of single solid waste components
and different solid waste mixtures under
varying compaction conditions.
c) Behavior of "standard" solid waste mixtures
under compaction conditions only touched
upon in the present project.
d) Compaction of exceedingly wet solid waste
materials.
e) Reduction of springback, and most
important,
f) Utilization of high pressure compaction as a
positive tool for advanced environmental
control.
In terms of total process development, all the
above factors are closely interrelated. To tailor a
lightweight press to solid waste compaction
requirements, divers material behavior patterns must
be considered. Testing of unusual solid waste input
mixtures might provide inputs that could enhance the
application potential of compaction equipment. To
enlarge upon the environmental control effects,
different analyses on material behavior are required,
and perhaps a different design of the press or
compaction process.
In addition, the promise of process improvement
offers a multiplication of benefits. A lightweight press
is low-cost and thus might improve the operational
options available to many solid waste disposal
jurisdictions. The service Ufe of many sanitary
landfills might be more than doubled and substandard
operations more easily eliminated. Solid waste bales
might effect the reclamation of arid areas and turn
the scars of ravaged land into topographic assets.
Further process developments promise to place
solid waste disposal beyond a mere negative
environmental control and transfer its efforts and
funds to the category of resources. In view pf this
opportunity, it is recommended that additional
efforts-estimated at about $480,000 and one year of
unencumbered work—be authorized as speedily as
possible.
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U. S. GOVERNMENT PRINTING OFFICE 1912 O - 461-084
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