Environmental Protection Technology Series
       FINE  SHREDDING  OF
MUNICIPAL  SOLID  WASTE
           U
      Industrial Environmental Research Laboratory
            Office of Research and Development
           U.S. Environmental Protection Agency
     Research Triangle Park, North Carolina  27711

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               RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five1 series. These five broad
categories were established to facilitate further.development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:

     1.   Environmental Health Effects Research
     2.   Environmental Protection Technology
     3.   Ecological Research
     4.   Environmental Monitoring
     5.   Socioeconomic  Environmental Studies

This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation  from point and non-point sources of pollution. This
work provides the new or  improved technology required  for the control and
treatment of pollution sources to meet environmental quality standards.
                    EPA RE VIEW NOTICE

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 policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

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                                   EPA-600/2-76-208

                                   July 1976
            FINE SHREDDING

                     OF

       MUNICIPAL SOLID WASTE
                     by

          K. P. Ananth and J. Shum

          Midwest Research Institute
            425 Volker Boulevard
         Kansas City, Missouri 64110
       Contract No. 68-02-1324, Task 39
        Program Element No. EHB533
     EPA Task Officer:  James D. Kilgroe

 Industrial Environmental Research Laboratory
   Office of Energy, Minerals, and Industry
      Research Triangle Park, NC  27711


                Prepared for

U.S. ENVIRONMENTAL PROTECTION AGENCY
      Office of Research and Development
            Washington, DC 20460

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                             ACKNOWLEDGMENTS
     The work presented in this report was performed for the Industrial En-
vironmental Research Laboratory-RTF of the Environmental Protection Agency
under Contract No. 68-02-1324, Task No. 39. The work was performed in the
Environmental Systems Section of Midwest Research Institute. Mr.  M. P.
Schrag, Head, Environmental Systems Section, was the program manager and
Dr. K. P. Ananth was the project leader.
Approved for:

MIDWEST RESEARCH INSTITUTE
L. J. Shannon, Assistant Director
Physical Sciences Division
30 July 1976
                                   iii

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                           TABLE OF CONTENTS
List of Figures 	  ..........  	  .....   vii

List of Tables	   viii

Abstract	   xi

Summary 	     1

Section

I.        Introduction.	     4

II.       Types of Shredding  Equipment	     5

               Hammermills.  .......  	     5
               Grinders  	     7
               Flail Mills	    10
               Manufacturer Supplied Design Data	    10

III.      Shredder Performance	    18

               Specific  Energy  Consumption	    18
               Product Size Distribution	    21
               Hammer Wear	    30

IV.       Shredder Selection	  ;	    32

V.        Shredder Costs	    34

               Capital Cost	    34
               Maintenance Costs	    37
               Operating Cost	    41
               Combined  Cost. ....  	  .....    45

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                          CONTENTS  (Concluded)

Section                                                            Page

VIo       Evaluation of Material/Energy  Recovery Systems.  ....    49

               Pyrolysis Systems	    49
               Combined Firing Systems	    52
               Summary.	    53

VII*      Conclusions and Recommendations  	    54

References	•    56
                                   vi

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                             LIST  OF FIGURES

Figure                            Title

   1      Horizontal  Shaft  Hammermill  	     6

   2      Vertical Shaft  Hammermill (Heil Company)	     8

   3      Cross-Section of  the  Eidal Grinder	     9

   4      Average Power Versus  Dry Feed Rate  for Primary and
            Secondary Grinding. .... 	    19

   5      Characteristic  Particle  Size Versus Specific Energy
            Consumption	    22

   6      Size Distribution of  Refuse From Various Shredders.  •  •    24

   7      Effect of Grate Size  on  Particle Size Distribution at
            Madison	    25

   8      Characteristic  Particle  Size Versus Grate Spacing  ...    27

   9      Effect of Moisture Content on Particle Size
            Distribution	    28

  10      Effect of Moisture Content on Particle Size
            Distribution	    28

  11      Changes in  Particle Size Distribution Due to
            Cumulative Hammer Wear	    29

  12      Power Requirement as  a Function of  Feed Rate and
            Characteristic  Particle Size Desired	    33

  13      Estimated Operating Cost for Various Shredder
            Capacities	    46

  14      Total Cost  Versus Rated  Capacity	    48

                                  vii

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                             LIST  OF TABLES

Table                             Title                             Page

  1       Advantages and Disadvantages of Some Shredder Types
            Based on Various  Criteria	    11

  2       1975 Survey of Shredders Used  (or to be used) for Size
            Reduction of MSW  in  the United States	    12

  3       Design Specifications  for Typical Horizontal Type
            Shredders Used for Processing MSW	    16

  4       Design Specifications  for Typical Vertical Type
            Shredders Used for Processing MSW	    17

  5       Product Size Distributions at  St. Louis Plant During
            Test Period 9/30/74  -  11/18/74	    23

  6       Production and Power Use at St. Louis Shredder During
   1         Test Period 9/30/74  -  li/18/74	    23

  7       Average Wear for Hammers and Grate Bars Under Different
            Speeds and Hammer Facing Conditions  .........    31
   I
  8       Initial Cost for Shredders of  Various Capacities. ...    35

  9       Initial Cost for Shredders of  Equivalent Size	    36

 10       Estimated Annualized Capital Cost	    38

 11       Comparison of Unit  Costs for Madison and Gainesville
            Plants	    39
                                 viii

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                          TABLES  (Concluded)

Table                             Title                             Page
 12       Maintenance Cost for Various  Components of Two
            Shredder Units	    40

 13       Maintenance Cost for (45  Mg/hr) Shredder Units as
            Provided by Manufacturers  	    42

 14       Maintenance Costs Observed at Madison and Gainesville  .    43

 15       Estimated Operating Cost  for  Primary Shredder Units  .  •    44

 16       Combined Cost of Shredding MSW.	    47

 17       Pyrolysis and Combined Firing Systems Investigated to
            Determine the Benefits  of Fine Shredding	•    49

 18       Size Distribution of Garrett  Secondary Shredded Solid
            Waste	    51

 19       Typical Size Distribution of  Shredded, Air Classified
            Refuse in St. Louis	    52
                                   IX

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                                 ABSTRACT
     This report presents an overview of equipment used for municipal  solid
waste (MSW) size reduction and discusses their performance  and cost  aspects.
Of the 11 basic types of equipment used for shredding  MSW,  only hammermills
and grinders find wide application. Evaluation of their performance  on the
basis of specific energy consumption as a function of  various  factors  such
as throughput, shaft speed, grate spacings, refuse moisture content, etc.,
indicates that:

     •  The specific energy consumption is independent of throughput for
        the same product size distributions and feed characteristics.  The
        power, however, is a function of throughput.

     •  Higher shaft speeds (rpm) produce finer size distributions and re-
        quire more energy for the same throughputs.

     •  Smaller grate spacings (exit clearances)  produce finer particles.

     •  Refuse moisture content has a definite effect  on specific energy
        consumption. The relationship is parabolic with increasing mois-
        ture content, first reducing specific  energy consumption and then
        increasing it. The specific energy consumption is a minimum  at 35
        to 407., moisture content.

     On the basis of available cost estimates, the initial  cost for  shred-
ders ranges from $3,528 to $6,174/Mg/hr or $3,200 to $5,600/ton/hr.  The an-
nualized capital cost is about $0.21/Mg or $0.19/ton.  Maintenance and  oper-
ating costs are estimated to be $0.33 and $1.74/Mg, respectively, for  a
shredder of capacity 9.07 Mg/hr (i.e.,  10 tons/hr). For a shredder of
90.7 Mg/hr capacity, maintenance and operating costs are estimated to  be
$0.77 and $0.55/Mg, respectively.

     Information on performance or cost benefits  of fine shredding is  cur-
rently lacking. The need for fine shredding in most material/energy  recovery
systems is currently dictated by process constraints and the benefits  may
be system specific. On a general basis, fine shredding is expected to  enhance
                                    xi

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energy recovery by Improving combustion efficiency and to enhance material
recovery due to increased effectiveness of separation devices.  These bene-
fits have not been documented as yet*
                                   xii

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                                 SUMMARY
     The Environmental Protection Agency (EPA) is supporting  development
of processes for recovery of material and energy from municipal solid
wastes (MSW). To accomplish this goal,  information is required on per-
formance and cost of MSW size reduction equipment since they  are criti-
cal for optimization of resource recovery systems.

     The objective of this task was to  (a) develop a  technology overview
of equipment used for municipal solid waste size reduction,  (b) develop
performance and cost data on MSW size reduction equipment, and (c)  eval-
uate performance/cost benefits from shredding* refuse to finer levels in
selected resource recovery systems.

     In conducting this task, Midwest Research Institute (MRI) reviewed
existing literature and contacted:   (a) manufacturers of equipment  for
size reduction of municipal solid waste;  (b) the Shredder Subcommittee of
the Waste Equipment Manufacturer's Institute of the National  Solid  Waste
Management. Association; (c) engineering consultants with expertise  in this
field; and (d) users of MSW size reduction equipment.

     Equipment used for size reduction  of MSW can be  categorized into 11
basic types. Of these, only hammermills and grinders  are extensively  used
and only these two are discussed in any detail in this report. Variations
in the design and operation of these equipment and their advantages and
disadvantages are also presented.

     The performance of shredders is discussed based  upon their, specific
energy consumption (kw-hr/Mg), product  size distribution,  and frequency
of replacements needed or machine wear. These performance.parameters  are
dependent upon factors such as throughput, grate spacings, motor shaft
speed (rpm), feed moisture content, feed size distribution, and feed  com-
position. Pertinent observations include:
   Waste Equipment Manufacturer's Institute has  designated  the  term  "Shred-
     der" to cover all mechanical equipment used to  break up  solid waste
     and recoverable materials to smaller sizes.  MRI has also used this
     designation throughout this report.

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     •  The specific energy consumption appears independent of throughput
        for the same product size distributions and feed characteristics.
    :    The power, however* is a function of throughput*

     •  Higher shaft speeds (rpm) produce finer size distributions and
        require more energy for the same throughputs.

     •  Smaller grate spacings (exit clearances) produce finer particles.

     •  Refuse moisture content has a definite effect on specific energy
        consumption. The relationship is parabolic with increasing mois-
        ture content, first reducing specific energy consumption and then
        increasing it. The specific energy consumption is a minimum at 35
        to 40% moisture content.

     •  The effect of refuse moisture content on product size distribu-
    ;    tion could not be determined because of the lack of data on this
        subject.

    , •  Increased hammer wear results in a coarser product.

    ; Cost data on shredders are scarce and even the limited information
varies from one manufacturer to another. Also, some cost quotations include
accessories and others do not. However, best estimates indicate that the
initial cost for shredders, with comparable accessories, ranges from $3,528
to $6,174/Mg/hr ($3,200 to $5,600/ton/hr). With an assumed initial cost of
$4,410/Mg/hr ($4,000/ton/hr) and 1,820 annual operating hours, the annual-
ized capital cost based on refuse processed annually is $0.21/Mg when the
equipment is amortized for 20 years at zero salvage value and 67« interest
rate. The corresponding cost per ton is $0.19. This cost is independent of
the Equipment's rated capacity. Maintenance and operating cost information
are available in the literature, but due to differences in cost accounting
practices much of the data are not amenable for direct comparison. Based
on best engineering judgment and conversations with knowledgeable persons
in the shredding field, the maintenance and operating costs were estimated
to be about $0.33 and $1.74/Mg, respectively, for a 9.07 Mg/hr capacity;*
for a capacity of 90.7 Mg/hr, they were about $0.77/Mg for maintenance
costs and $0.55/Mg for operating costs. It appears that maintenance costs
increase with unit size but we have not been able to establish the rea-
sons; for this relationship due to lack of data.

     Material/energy recovery systems such as pyrolysis and combined fir-
ing (coal-refuse) were evaluated to determine if cost or performance bene-
fits; may be derived from shredding refuse to finer levels. It appears that


*  A capacity of 9.07 Mg/hr corresponds to 10 tons/hr.

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process .constraints, more than anything else,  dictate  the  need  for
shredding and the major benefit,  as such,  may  be  from  an increase in  the
combustion/reaction efficiency. The Occidental Petroleum Company, Monsanto
Corporation, and the Union Carbide Corporation all  shred the  refuse prior
to using it in their pyrolysis systems, but  they  have  not  been  able to
provide us any information on cost or performance benefits. The St. Louis
demonstration project which fires coal and refuse in a utility  boiler also
shreds the refuse and classifies  it prior  to feeding it  into  the boiler.
No quantitative data are reported on the benefits of fine  shredding the
refuse.

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                               SECTION I

                              INTRODUCTION
     Material and/or energy recovery processes from municipal solid waste
have grown in importance recently due to (a) the search for new energy
sources, (b) increased concern in the location and presence of landfills,
and '(c) the possibility of recovering nonrenewable mineral resources.  In-
trinsic to these processes is the need for size reduction of MSW.

     At present there is little published information on the cost  and  per-
formance of equipment for MSW size reduction. This project was undertaken
to provide an overview of the technology behind shredders and to develop
cost and performance data. Also included in the project was the evalua-
tion of existing material/energy recovery systems to determine the cost/
performance benefits of fine shredding.

     A literature search was first undertaken to identify gaps in  the
data base. In addition, shredder manufacturers, the National Solid Waste
Management Association, users of MSW size reduction equipment and  engineer-
ing consultants with expertise in this field were contacted. The technology
overview is presented in the next section. This is followed by sections on
performance, costs, and evaluation of existing material/energy recovery
systems* Conclusions and recommendations based on this study are also
presented.

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                              SECTION II

                      TYPES OF SHREDDING EQUIPMENT
     Size reduction or shredding of municipal solid waste  is  the mechani-
cal process of breaking up solid waste and recoverable materials to smaller
sizes. There are, at present,  11 basic types  of  shredding  equipment which
are commercially available. These are:  crushers,  cage disintegrators,
shears, grinders, cutters and chippers,  rasp  mills, drum pulverizers, disk
mills, wet pulpers, hammermills, and flail mills. *-|2/ Of these, only ham-
mermills and grinders have been used widely in the United  States for the
size reduction of MSW^' Therefore, this discussion will be devoted mainly
to these two types of shredders. A brief description of the flail mill is
also included at the end, since it is a  new concept.^'

HAMMERMILLS

     Hammermills are currently the most  popular  type of shredder equip-
ment used for MSW size reduction. A hammermill consists of a  radial rotor
or shaft with hammers attached to the rotor by means of the hammer pins.
These pins are long rods which, in effect, lace  the hammers to the rotor
by running them through the holes in the rotor and hammers. When the en-
tire assembly is rotating, the hammers fly perpendicular to the rotor.
The moving parts are enclosed in a heavy duty housing which may be lined
with abrasion resistant steel structures. Input  materials  are shredded by
impact, attrition and shearing forces induced by the hammers. Sometimes
stationary breaker plates or cutter bars are  placed inside the housing
to assist shredding.

     There are two basic types of hammermills. These are the  horizontal
shaft type and the vertical shaft type.  The horizontal shaft  hammermill
has the shaft or rotor mounted horizontally and  supported  on  each end.
The rotors can be designed to rotate in  either direction.  Input solid
waste is generally fed from the top assisted  by  gravity and the rotor
torque. Force feed at the side of the hammermill has also  been used. A
schematic diagram of a horizontal hammermill  is  shown in Figure 1.

     The hammers attached to the rotor are either of swinging or rigid
type. The swinging hammers are mounted on pins and are free to rotate.

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                                Input
                                   Grate Bars
                   J   Output    Conveyor
C
Figure  1.   Horizontal shaft hammermill,

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This design reduces hammer damage. However,  when the  hammers  become  en-
tangled with the input material and are not  allowed to  swing  freely,  se-
vere imbalance problems can arise. For both  types of  hammers,  shapes  vary
from sharp choppers to blunt rectangular beaters. The latter  are most
often used for solid waste size reduction.

     Output material size in a horizontal type hammermill  is  controlled
by the size of the openings of the grate. The grate is  located across the
output opening of the hammermill.  Input material remains in the hammer-
mill until it is small enough in at least two dimensions to fall through
the grate openings.

     Most manufacturers of horizontal shaft  hammermills recommend direct
coupling of the motor and the shredder rotor shafts.  This  procedure  is
generally the simplest and least expensive connection method.

     The vertical shaft hammermill has the rotor placed in a  vertical po-
sition. Input material enters at the top and progresses downward parallel
to the shaft axis. Both types of hammer design (swinging or rigid) have
been used with the vertical hammermill. A typical vertical shaft hammer-
mill is shown in Figure 2.

     The vertical shaft hammermill has no grate system at  the discharge
section of the machine. Particle size control is effected  by  the decreas-
ing clearance between the hammer tips and the housing from top  to bottom.
However, output particle size increases as hammers and housing  plates
wear.

     Direct coupling of the motor  shaft to the vertical shaft is not  prac-
tical. Generally a gear or belt drive system is used. While the belt  drive
permits some flexibility in motor  location,  the gear  drive normally re-
quires additional support equipment and thus increases maintenance require-
ments.

GRINDERS

     Another common type of equipment used for size reduction of MSW  is
the vertical shaft grinder. Figure 3 illustrates a typical vertical grinder.
The principle adopted in the design of such  a grinder differs from that of
the hammermill in that size reduction is accomplished by a set  of gearlike
teeth installed in a rotor which fits in a stationary ribbed  housing. The
input material introduced into the upper part of the  machine  is first ex-
posed to a set of breaker bars by  means of which large objects  are torn
apart. The material then enters the space between the rotor teeth and the
housing ribs. Size reduction occurs in this  part of the machine due to the

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Conical
Pre-breaking
Section
                                 Rejection
                                 Section
                                                              Exit
                                                              Section
        Grinding
        Section
        Figure 2.  Vertical  shaft hammermill  (Heil Company).

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Figure 3.  Cross-section of the Eidal grinder,

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induced shear and the mutual self-comminution interaction between the var-
ious types of materials^'

     The space between the rotor and the housing is tapered and this de-
creasing clearance geometry controls the size of the product leaving the
grinder. The main advantages of the grinder are its low speed (~ 400 rpm)
and no objects are rejected as in a hammermill.

FLAIL MILLS

     A third type of shredder which has recently been applied to MSW is
the' flail mill. The shredding is done using articulated flails mounted on
opposed rotors. Since a flail mill passes all input materials quickly with-
out repeated impacts, energy and cost requirements are much lower than in
conventional shredders where solid waste is ground or forced through a
grate system. A power consumption of 5.1 kw-hr/Mg (6.2 HP-hr/ton) of refuse
has been reported by one manufacturer^'  Another advantage of the flail
mill is that it can operate at maximum capacity without large variations
in load due to a more uniform impacting situation^'  Flail mills have been
used as primary shredders in solid fuel and pyrolysis process systems de-
veloped by Combustion Equipment Associates, Inc., and Arthur D.  Little,
     Table 1 summarizes the advantages and disadvantages  of the shredders
discussed above and Table 2 presents a listing of shredding facilities
which are now in operation, or for which ground has been  broken through-
out i the United States.-^'  Table 2 includes shredder type and also the  rated
capacity. The original listJ-'  has been modified to indicate only those
shredder systems which shred MSW for energy and/or resource recovery.

MANUFACTURER SUPPLIED DESIGN DATA

     Several manufacturers of shredders were contacted to obtain design
specifications for their systems. Most of them responded  with  company bro-
chures and provided additional information. Design data for some systems
had to be obtained from the open literature. Tables 3  and 4 are listings
of design specifications that were available to us. The data are grouped
by shredder type (horizontal or vertical) and by rated capacity.
                                   10

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         Table 1.  ADVANTAGES AND DISADVANTAGES  OF SOME SHREDDER TYPES  BASED  ON VARIOUS  CRITERIA
Application
                      Horizontal hammermills
Wide range
                              Vertical
                             hammermills
Wide range
                         Grinders
Wide range
    Flail mills

Principally limited
to primary stage
size reduction
Handling of hard
  objects
Particle size
   (product)
  control
Difficult and causes
jamming
Can be well controlled
by adjusting grates
Rejected ballisti-
cally or passed
through without
much size reduc-
tion

Less uniformity
in particle size
distribution
Not rejected
Can be well
controlled
Passed through with-
out much size reduc-
tion
Moderately uniform
Wear rate             High
Power requirement     High
                         Low                  Low

                         Lower than hori-     High
                         zontal hammermills
                                       Low

                                       Low
Auxiliary equipment
  needed
None, if direct
driven
Requires gear or
belt drive to
couple with motor
Requires gear
or belt drive
to couple with
motor
None

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      Table 2. 1975 SURVEY OF SHREDDERS USED (OR TO BE  USED)  FOR SIZE  REDUCTION OF MSW IN THE UNITED STATES
N>
Location
California
Los Gatos
Menlo Park
San Diego
Connecticut
Bridgeport
Florida
Ft . Lauderdale
Illinois
Type of
Start-up date shredder
1969 Horizontal shaft
3 units - primary,
secondary, terti-
ary
March 1973 Vertical
March 1976 Horizontal
hairanermill
August 1976 2 horizontal
hannnermills
1973 Horizontal

Type of
shredder
waste
Municipal, both
packer truck and
bulky waste
Municipal and
packer truck
Municipal
Municipal
Municipal

Rated
capacity
27 Mg/hr
(30 tons/hr)
for whole
system
2.7 Mg/hr
(3 tons/hr)
32 Mg/hr
(35 tons/hr)
68 Mg/hr
(75 tons/hr)
each
366 m/hr
(400 yd/hr)

Disposition
of waste
Recycling and
energy recovery
Power generation
Pyrolysis
Generate elec-
tricity
Incineration/
landfill

      Chicago
1971
Horizontal
Municipal
27 Mg/hr       Incineration
(30 tons/hr)

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                                           Table 2.   (Continued)
    Location
Start up date
Illinois (Concluded)

Chicago            1975
Chicago


Chicago



Iowa

Ames


Pleasant Hill


Maryland

Baltimore



Mas sachus ett s

Marlboro
June 1975
October 1975
June 1975
1973
1974
     Type of
     shredder
                 2 vertical
Vertical
Horizontal
2 horizontal
hammermills
2 horizontal
    Type of
    shredder
     waste
                     Secondary  grind
Secondary grind
Municipal and
oversized bulky
waste
Municipal
Horizontal, single   Municipal
direction
November 1973    Horizontal
Municipal, in-
dustrial over-
sized bulky
                     Municipal
 Rated
capacity
 Disposition
  of waste
                   54 Mg/hr       Fuel supplement
                   (60 tons/hr)
                   each
54 Mg/hr
(60 tons/hr)

68 Mg/hr
(75 tons/hr)
Energy recovery
Btu recovery
45 Mg/hr
(50 tons/hr)

18 Mg/hr
(20 tons/hr)
45 Mg/hr
(50 tons/hr)
each
Generate elec-
tricity

Composting and
pyrolysis
Pyrolysis
                   27 Mg/hr       Incineration
                   (30 tons/hr)

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                                           Table 2.  (Continued)

Location
Missouri
St. Louis
St. Louis

St. Louis

New York
Buffalo
Pennsylvania
Type of
Start up date shredder
1971 Horizontal
April-December 7 horizontal
1976 primaries

April-December 7 horizontal
1976 secondaries

1970 Horizontal

Type of
shredder
waste
Municipal
Packer and
oversized bulky
waste
Primary shedded
materials
ferrous removed
Municipal

Rated Disposition
capacity
68 Mg/hr
(75 tons/hr)
91 Mg/hr
(100 tons/hr)
each
86 Mg/hr
(95 tons/hr)
each
184 cu m/hr
(240 cu yd/hr)

of waste
Power generatioi
Energy recovery
and ferrous
recovery
Energy recovery

Incineration

Harrisburg
York
December 1970    Horizontal
1975
Horizontal
                     Municipal
Municipal,
packer truck
73 Mg/hr
(80 tons/hr)

23 Mg/hr
(25 tons/hr)
                                  Incineration
Incineration

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                                            Table  2.   (Concluded)


Location Start up date

Type of
shredder
Type of
shredder
waste

Rated
capacity

Disposition
of waste
Washington

Cowlitz County     1975


Longview           1971



West Virginia

South Charleston   1975
Wisconsin
Milwaukee
August 1976
                                    Horizontal
                                    Horizontal
                                    Vertical
2 horizontal
primaries
                                      Municipal
                                      Municipal  and
                                      pulp and paper
                                      mill waste
                                      Municipal
Packer and
oversized bulky
waste
                                        45  Mg/hr
                                        (50 tons/hr)

                                        45  Mg/hr
                                        (50 tons/hr)
                                        14 Mg/hr
                                        (15 tons/hr)
                                                                           73 Mg/hr
                                                                           (80  tons/hr)
                                                                           each
                                  Power generation
                                  In plant incin-
                                  eration
                                  Pyrolysis
Energy recovery
and ferrous
separation

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                                             Table  3.   DESIGN SPECIFICATIONS FOR TYPICAL HORIZ10NTAL TYPE SHREDDERS USED FOR PROCESSING  MSW
Capacity
(Hg/hr)
0.9-1.8

1.8-4.5

4.5-9.1

6.3

7.3
9.1

9.1

9.1-14

14

14-18

18

18
18-27

22
23

27

27
27-36

29
32

36
36-45

45

45

50

73
91

91

109
136

(tons/hr)
1-2

2-5

5-10

7

8
10

10

10-15

15

15-20

20

20
20-30

24
25

30

30
30-40

32
35

40
40-50

50

50

55

80
100

100

120
150

Manufacturer
Pennsylvania Crusher
Corporation
Pennsylvania Crusher
Corporation
Pennsylvania Crusher
Corporation
Jeffrey Manufacturing
Company
Gondard Mill
American Pulverizer
Company
Gruendler Crusher and
Pulverizer Company
Pennsylvania Crusher
Corporation
Jeffrey Manufacturing
Company
Pennsylvania Crusher
Corporation
American Pulverizer
Company
Williams Hammermills
Pennsylvania Crusher
Corporation
Hammermills, Inc.
Jeffrey Manufacturing
Company
American Pulverizer
Company
Williams Hammermills
Pennsylvania Crusher
Corporation
Hanmennllls, Inc.
Jeffrey Manufacturing
Company
Hamne trail Is, Inc.
Pennsylvania Crusher
Corporation
American Pulverizer
Company
Gruendler Crusher and
Pulverizer Company
Jeffrey Manufacturing
Company
Hairmermills, inc.
American Pulverizer
Company
American Pulverizer
Company
Hammermills, Inc.
American Pulverizer
Company
Model
No.
S12024

S13030

S13640

432


4200

48-4

SH3640

548

SH3666

48-50

GA-70
SH4454

4260
748

60-50

K-460
SH4478

6060
770

6080
SH5484

60-90

60x84

990

74104
72-72

72-84

96104
96-90

Power Speed Feed opening Dimensions (cm)ji'
(kw)
19

45

93

75

112


186

149

186

224

298-373

298
298

447
298

522-746

298
447

597
373

746
597

746

932

559

1,490
1,120-1,490

1,120-1,490

2,240
2,240-3,730

(HP) (rpm) (cm) (in.) Length Width Height
25 41 x 64 16 x 25

60 64 x 89 25 x 35

125 74 x 112 29 x 44

100 81 32

150 1,150
79 x 140 31 x 55 183 239 124
(72) (94) (49)
250 1,200

200 64 x 102 25 x 40

250 122 48

300 64 x 152 25 x 60

400-500 900 127 x 137 50 x 54 259 297 185
(102) (117) (73)
400 1,200 61 x 178 24 x 70
400 81 x 142 32 x 56

600
400 122 48

700-1,000 900 122 x 132 48 x 52 262 305 229
(103) (120) (90)
400 800 142 x 160 56 x 63
600 81 x 203 32 x 80

800
500 178 70

1,000
800 107 x 213 42 x 84

1,000 720 122 x 234 48 x 92 262 406 229
(103) (160) (90)
1 , 250 894

750 229 90

2,000
1,500-2,000 900 173 x 193 68 x 76 343 462 312
(135) (182) (123)
1,500-2,000 900 173 x 224 68 x 88 343 493 312
(135) (194) (123)
3,000
3,000-5,000 720 213 x 234 84 x 92 437 503 371
(17?) (198) (146)
Weight
(kg) O-b^ Reference
816 1,800 1

2,720 6,000 1

3,630 8,000 1

1

10
8,620 19,000 Company bulletin

11

6,120 13,500 1

1

5,670 12,500 1

18,100 40,000 Company bulletin,
private communication
8,940 19,700 19
9,070 20,000 1

Company bulletin
1

28,600 63,000 Company bulletin,
private communication
15,200 33,500 19
12,700 28,000 1

Company bulletin
1

Company bulletin
21,800 48,000 1

47,600 105,000 Company bulletin, 6

14

1

Company bulletin
86,200 190,000 Company bulletin,
private communication
95,300 210,000 Company bulletin.
private communication
Company bulletin
134,000 925,000 Company bulletin,
private communication
a/  Except numbers in parenthesis, which  are  in  inches.

-------
                            Table 4.   DESIGN  SPECIFICATIONS  FOR TYPICAL VERTICAL TYPE SHREDDERS USED FOR PROCESSING MSW
Capacity
0.9-3.6
14
14
14-32
18
27-50
36-41
45
54
68
73-91
(tons/hr)
1-4
15
15
15-35
20
30-55
40-45
50
60
75
80-100
The
The
Manufacturer
Carborundum Company
Heil
Company
Model
No.
100
42-D
Tollemache Mill
The
The
The
The
The
The
The
The
Carborundum Company
Heil
Company
Carborundum Company
Heil
Heil
Heil
Heil
Heil
Company
Company
Company
Company
Company
400
42-F
1000
72
92
92
92
92
Power Speed Feed opening
(kw)
75
149
149
298S/
186
746k/
373
373
559
746
746
(HP) (rpm) (cm) (in.)
100 415 132 x 76 52 x 30
200 76 x 122 30 x 48
200 1,300
40Q§/ 390 152 x 152 60 x 60
250 107 x 152 42 x 60
l.OOQk/ 369 152 x 224 60 x 88
500
500 122 x 213 48 x 84
750 122 x 213 48 x 84
1,000 122 x 213 48 x 84
1,000
Weight
(kg) (lb)
6,100 13,450 Company
Private

17,200 38,000 Company
Private
4,170 92,000 Company
Private
Private
Private
Private
Private
Reference
bulletin,
1
communication,
10
bulletin,

1
communication ,
bulletin,
1

1


1

coiriminication
communication,
communication ,
comnunication ,
1
1
1
communication
aj  Uses two 149 kw  (200 HP) motors.
W  Uses two 373 kw  (500 HP) motors.

-------
                              SECTION III

                          SHREDDER PERFORMANCE
     Performance data for some shredder units have been reported by
Ruf,-§' Gawalpanchi et al.,.5' and Reinhardt et al*i2'  A more systematic
investigation of shredder performance and the effect of various paramet-
ers on performance has been recently reported by Trezek et al«  *
Trezek's study-i=' was conducted with a Gruendler-Model 48-4 hammermill
with a design capacity of up to 9.1 Mg/hr (10 tons/hr). The effects of
feed rate, grate or extraction spacing and hammer speed (rpm) on product
size distribution and specific energy consumption were investigated under
controlled laboratory conditions. Also, particle size distributions of
shredder refuse from different types of shredders are reported..^/ A math-
ematical simulation of the comminution process in a swing hammermill using
four matrix models is also available.—  The models can be used to predict
product size distributions for primary, secondary, and tertiary grinding
processes. The difficulty, however, is to obtain selection and breakage
functions for the models from first principles.

     Our evaluation of shredder performance is based on information
contained in Refs. 11 and 12 and data obtained from field studies in
Gainesville^'  Madison,"? *•()/ and st. Louis^i^:' We have characterized
shredder performance in terms of specific energy consumption, product size
distribution, and machine wear or frequency of replacements required. Fac-
tors such as feed throughput, shredder/hammer design, rotor speed (rpm),
feed moisture content, feed size distribution and feed composition, which
affect shredder performance are also discussed.

SPECIFIC ENERGY CONSUMPTION

     Factors which can affect the specific energy consumption (kw-hr/Mg)
are shredder/hammer design, rotor speed, and feed moisture content, feed
size distribution, and feed composition. As shown in Figure 4, feed through-
put has minimal effect on specific energy consumption for both primary and
secondary grinding except at very low feed rates such as those below 1.8
Mg/hr (2 tons/hr) JJ:/ At feed rates below 1.8 Mg/hr (2 tons/hr) the specific
energy consumption is not a constant.-^' In Figure 4, the output from pri-
mary grinding was used as the feed for secondary grinding. No size data
were reported.

                                   18

-------
   90
    80
    70
   60
 o

 o
 ..  50
C£
LLI



O
O  40

<
Di
LU
   30
   20
    10
                            (DRY)  FEED  RATE,  tons/hr


                         2345
                          I
                                  T
T
I
                                                       PRIMARY

                                                       GRINDING
                                             Specific  Energy

                                             Consumption = 17.9 kw"hr
                                                               Mg
                                                      SECONDARY

                                                      GRINDING
 7

^120
                                                                         110
                                                                         100
                                                                         90
                                                                         80
                                                                         70
                                                 Specific  Energy

                                                 Consumption =6.1
                                                                 kw-hr ~

                                                                  Mg
                           I
                                                I
                                                                         50
                                                                         40
                                                                         30
                             20
                                                                         10
                           234

                            (DRY) FEED RATE, Mg/hr
         Figure 4.  Average power versus  dry  feed rate  for primary

                      and secondary grinding.—'
                                                                              01
                                  o
                             60   «*•
                                                                              O
                                                                              LLJ
                                      19

-------
     The type of shredder used can alter the specific energy consumption.
For instance, horizontal-shaft hammermills generally require more energy
since particles must be ground fine enough to pass through the grate open-
ings. The Madison study^ilO'  shows that the Gondard mill (i.e., horizontal
shaft) has a specific energy consumption of 13.8 kw-hr/Mg (16.8 HP-hr/ton)
whereas the Tollemache mill (i.e., vertical shaft) only needs 7.9 kw-hr/Mg
(9.7 HP-hr/ton). The machines used in the above study were of comparable
size and were operated under comparable conditions. The use of a flail
mill results in a more drastic reduction in the specific energy consump-
tion. A value of 5.1 kw-hr/Mg (6.2 HP-hr/ton) is reported for a flail
millj/

     Experience with the Tollemache mill at Madison indicates that the
number of hammers, their size and arrangement can affect specific energy
consumption. The original design of 54 hammers when replaced with 34 ham-
mers arranged in a more efficient manner actually increased production at
Madison, resulting in a decrease in specific energy consumption..!]?-'

     For constant feed throughputs and feed conditions, any increase in
rotor speed will increase the specific energy consumption. It is reported—-
that an increase in speed from 790 to 1,200 rpm at a feed rate of 4.5 Mg/hr
(5 tons/hr) raises the specific energy consumption from about 11.0 to 18.7
kw-hr/Mg (13.4 to 22.8 HP-hr/ton) on a dry basis. No additional data are
available to determine the exact relationship. Higher speeds, however, have
the benefit of generating finer particles as will be shown in the next sec-
tion.

     Variations in feed size distribution and feed composition will  in-
fluence specific energy consumption. Larger particles and a larger percent-
age of high tensile strength materials in the feed stream could increase
the specific energy consumption. For example, a secondary shredder which
is preceded by a magnetic separator and an air classifier after the  pri-
mary unit should consume less energy than one without these systems  before
it. At the present time there are no data to document this expectation.

     Trezek's studyJL^/ and the Madison study-i^'  both report the influence
of refuse moisture content on the specific energy consumption. Trezek-=='
indicates that for a horizontal shredder the specific energy consumption
generally decreases with increasing moisture content up to a certain point
and then increases with moisture content beyond that point. Typically,
minimum energy consumption is observed between 35 and 407« moisture.  The
Madison study showed that for a vertical Tollemache hammermill, the  winter
refuse having 24% moisture required 12.0 kw-hr/Mg (14.6 HP-hr/ton) in con-
trast to the summer refuse with 367o moisture which required only 9.7 kw-hr/
Mg (11.8 HP-hr/ton). The effect of higher moisture contents (> 36%)  on
                                    20

-------
specific energy consumption are not reported in the Madison study.  There-
fore, no comparisons can be made between Refs. 10 and 12 for moisture con-
tents greater than 36%.

     The specific energy consumption is also a function of product  size,
and was found to be related to a characteristic particle size,  XQ ,  which
corresponds to a 63,2% cumulative passing in a Rosin-Rammler distribution
of the
                     y(x) = 1 - exp
In the above equation,  y(x)  is the cumulative percent passing  screen
size  x  and  n  is the slope of the line  ln[l/(l-y)]  versus   x  on log-
log coordinates. The relationship between characteristic particle size,
xQ , and specific energy consumption is illustrated in Ref.  12 and is shown
in Figure 5. In the same figure we have also shown the range of  character-
istic particle sizes,  xo ,  and the range of specific energies consumed  to
produce those sizes in the St. Louis study.-=-t'  Tables 5 and  6 were used  to
establish the St. Louis range of characteristic particle sizes and the
range of specific energies,  respectively. It can be seen from Figure 5
that, for a characteritic size range of 1.2 to  1.4 cm (i.e., values ob-
served in St. Louis), the specific energy consumption should lie between
21.8 and 23.8 kw-hr/Mg (26.6 and 29.0 HP-hr/ton) according to the rela-
tionship established by Trezek^i?-' The actual energy values  observed at
St. Louis for this particle size range lie between 21.1 and  23.5 kw-hr/Mg
(25.6 and 28.7 HP-hr/ton) (see Table 6).  The individual points obtained
in St. Louis are also plotted in the figure showing good agreement between
values predicted by theory and those actually observed.

PRODUCT SIZE DISTRIBUTION

     The size distribution of shredded refuse from various grinders is
shown in Figure 6. However,  these distribution  curves cannot be  compared
since they can be affected by grate spacing,  feed characteristics,  rotor
speed and hammer wear and these differences in  operating conditions are
not well identified. Variation in feed rate has only a minor effect on
product size distribution.^'

     The grate spacings of the Gondard hammermill (7.3 Mg/hr or  8 tons/
hr) at Madison were varied from 8.9 to 15.9 cm  (3-1/2 to 6-1/4 in.) and
the product size was determined. Figure 7 shows the product  size distri-
butions obtained for the various grate spacings
                                   21

-------
      0.1
                    CHARACTERISTIC PARTICLE  SIZE, X0 (in.)
                0.2        0.4   0.6  0.8 1.0       2.0
4.0    6.0
_
 i
O
UJ
z
   30
   26
   22
    18
    14
                 T
                                   I    I    I
 I      _
         Predicted by Trezek
=   10
U
LU
Q_
    2
    0
                 _L
                                           nEidel 100
                                           A Heil-Gondard
                                           O Gruendler
                                           • Rabco
                                         XQ - 15.2 cm (6.0 in.)
                                               Corresponds to the
                                               Zero Energy
                                               Reference
                                           ® Values Observed
                                               in St. Louis
                                               Study
                                                                 Ref.
                                                                 12
                0.5        1.0                      5.0         10
                     CHARACTERISTIC PARTICLE  SIZE, X0 (cm)
         36

         32

         28

         24

         20

         16

         12

         8

         4

         0
                                                                             c
                                                                             O
                                                                             Q_
                                                                             X
O
LU
Z
                                                                             U
                                                                             LU
         Figure 5.  Characteristic particle size versus specific
                                     •    1 ? /
                      energy consumption.^^'
                                     22

-------
     Table 5.  PRODUCT. SIZE DISTRIBUTIONS AT ST. LOUIS PLANT DURING
                   TEST PERIOD 9/30/74 -
                                    9-30
                                                  Week of
                                            10-7    10-14    10-21    11-18
% larger than 6.4 cm (2.5 in.)
70 less than 6.4 cm (2.5 in.)
7o less than 3.8 cm (1.5 in.)
7o less than 1.9 cm (0.75 in.)
7o less than 0.95 cm (0.375 in.)
7o less than 0.47 cm (0.187 in.)
7o less than 0.24 cm (0.094 in.)

Characteristic size
  x0 (cm)*/
0
100.0
97.0
72.1
45.1
23.7
11.6
0.6
99.4
96.4
71.6
45.8
28.2
18.1
0
100.0
98.1
78.0
54.2
33.1
20.0
0
100.0
97.4
72.8
47.1
30.3
16.1
0
100.0
97.2
70.0
42.3
24.3
17.0
                                      1.4    1.3     1.2      1.3      1.4
                                     (0.56)  (0.52)   (0.48)   (0.50)   (0.56)
a/  Characteristic size was computed using method described in Ref.  12.
      Values in parentheses are in inches.
        Table 6.  PRODUCTION AND POWER USE AT ST. LOUIS SHREDDER
                DURING TEST PERIOD 9/30/74 -
Week of

 9-30
10-7
10-14
10-21
11-18
Raw refuse
processed^'
                              Electrical power
                                  used£'
                                                     Specific energy
             (Mg)    (tons)   (kw-hr)   (HP-hr)   kw-hr/Mg    HP-hr/ton
1,022
  680
  522
  571
  792
1,127
  750
  575
  629
  873
21,539
14,561
12,286
12,893
17,140
                          28,884
                          19,526
                          16,476
                          17,290
                          22,985
                                                    21.1
                                                    21.4
                                                    23.5
                                                    22.6
                                                    21.6
                                                                 25.6
                                                                 26.0
                                                                 28.7
                                                                 27.5
                                                                 26.3
a/  Mg (tons) processed reported here are presented on a dry weight
      basis.
t>/  Taken as 63% of total plant power. (The total rated horsepower of
      the shredder, all conveyor motors, magnetic drum, etc., amounts
      to 1,981.4 and the rated horsepower of the shredder alone is
      1,250 or 6370 of total. This assumes that all components are pro-
      portionately loaded.)
                                     23

-------
      0.01
                              SCREEN SIZE {in.)

                           0.1                    1.0
O
z
oo
GO
<
u
                                                    Heil-Gonard
                                                    Hammermill
                           555RPM
                           790 RPM
                        1200RPM
                              Rabco Grinder
          Gruendler
          Hammermill
                                        1.0

                                SCREEN SIZE (cm)
                                                               10
  Note:  Data for 555,  790,  and 1,200  rpm were  obtained  from a  laboratory
           unit whereas others  were obtained  from  field  units
   Figure 6.   Size distribution of  refuse  from various  shredders.
                                                                 12.147
                                   24

-------
  O
     100
      80
        10
                     PARTICLE SIZE (in.)
                     1.0              0.1
«  60
  g  40
  Z  20
  LU
  E   0
                     1-3-1/2" Grate
                         5" Grate
         -6-1/4" Grate
             10
                           1.0              0.1
                      PARTICLE SIZE (cm)
0.01
Figure 7.  Effect of grate size on particle  size distribution
             at Madison..I5/
                             25

-------
Trezekl?./ has shown, graphically, a relationship between grate spacing
and a characteristic particle size,  xo , which has been discussed in
the earlier section. This relationship has been reproduced in Figure 8.
Product size distributions obtained from the St. Louis studyJLz' were used
to obtain the range of characteristic particle size for the St. Louis
shredder, as shown earlier in Table 5. This range was then plotted in
Figure 8 to compare the grate spacing predicted by Trezek's curve with
that actually observed in St. Louis. It can be seen from Figure 8 that
the predicted grate spacing lies between 4.1 and 5.1 cm (1.6 and 2 in.),
whereas the grate spacing in St. Louis was a 7.6-cm (3-in.) square. This
disagreement could be due to differences in raw refuse composition. Also,
the grate spacings reported by Trezekil' were rectangular in shape with
the indicated dimension being in a direction perpendicular to the axis
of the mill shaftJL^'  In summary, experience, as well as Refs. 12 and 15,
indicates that smaller grate spacings yield a finer product size distri-
bution.

     Two contrasting observations are reported regarding the effect of
moisture content on product size distribution."i*-2/ The Madison study found
the product size to be finer and more uniform with increase in moisture
content.^'  This result is shown in Figure 9. The range of moisture content
investigated was between 46 and 927o. Trezekil' varied the moisture content
between 37 and 6370 and found increasing moisture content to result in a
coarser size distribution as shown in Figure 10.

     Rotor speed is generally believed to have a positive effect on prod-
uct size distribution with higher speeds producing a finer product. Trezeklf.'
has investigated product size distributions with a 10 tons/hr Gruendler ham-
mermill at speeds of 1,200, 790, and 555 rpm using grate bars with 6.4 cm
(2-1/2 in.) openings.  The grates were rectangular in shape with the 6.4 cm
(2-1/2 in.) opening being perpendicular to the shaft;  the opening parallel
to the shaft was about 15.2 cm (6 in.).—'  For grinding speeds of 1,200,
790, and 555 rpm the corresponding average values of the characteristic
particle size (XQ)* were 2.0,  2.7, and 2.2 cm (0.78, 1.08, and 0.88 in.).—'
Trezek claims that decreased speeds should usually produce a coarser prod-
uct and increased speeds a finer product. However, at the two lower speeds
(790 and 550 rpm) cited above,  this is not the case. He has hypothesized
that when a minimum speed is attained, the speed variable does not partici-
pate dominantly in the overall  size reduction process.JLr.'

     Hammer wear increases output particle size by progressively enlarging
the clearance between the hammer tips and the housing. Figure 11 shows the
effect of hammer wear on particle size distribution^/
*  The characteristic particle size,   xo  ,  has been defined earlier on
     page 21.

                                   26

-------
             CHARACTERISTIC PARTICLE SIZE,  XQ (Inches)
0
1—
X 16
LU
<*-=• 14
°ll2
Zu 10
<| 8<
% < 6
LU
i j j _j
i— O 4
^ 2
0 n
1 0.2 0.4 0.6 0.8 1.0
i i i i |

A
/
7
Actually Used in St. Louis W /
/ /

_ r- Predicted by Trezek !=/ >/•
f *~^^
~ P ^^^\^
a 	 ]
' , '!' 1
2.0 4.0 6.
i i

—

—
—
0 Eidel 100 ^| Referenc-e
A Heil-Gondard \ ^
• Gruendler J ~

—
i i
0
7 ^_
—
6 UJ -^

5 O -5
c
4 ~z^
3\J ^_
< Z
Q- <
^ ^c
UJ uj

°
            0.5        1.0           2.54      5.0        10.0
                CHARACTERISTIC PARTICLE SIZE X0, (cm)
Figure 8.   Characteristic particle size versus grate spacing.
                                                           12/
                             27

-------
               z
               o   1
               x 100
               LLJ
               N  80
              SIEVE SIZE (Inches)
                1.0       0.10
                                     0.01
               to
                  60
« 40
LU

E 20


Z"  0
LU

-------
         100
          80
             0
       LJJ
       z
          60
       u 40
          20
           0
     TONS MILLED

100   200    300   400
              I
500
                   100     200     300

                        Mg MILLED
                      400
Figure 11.  Changes in particle size distribution due to

              cumulative hammer wear.—
                              29

-------
The data in Figure 11 clearly show the time dependency.  The curves were
described by the function  Y = b0 + biexp(-b2t)  where  Y  is the weight
percent of particles finer than the stated mesh size,   t  is the cumula-
tive refuse milled (in Mg) since new hammers were installed, and the  b's
are empirical parameters^' It is also reported that hammer, wear was a
more significant variable than moisture content in affecting particle
size distribution..?'

     Secondary and tertiary shredding obviously produce  a finer product
size distribution than primary shredding.  This fact has  been well docu-
mented in the literature J-Lj-LL'  The performance of the  later stages will,
however, vary with the amount of air classification or heavies separation
that the feed undergoes after the primary  shredder.

HAMMER WEAR

     Hammer wear is closely related to shredder performance. Its effect
on product size distribution has been discussed in the previous section.

     Another aspect of "performance" is the need for replacements and
maintenance of hammer tips and related components. In  general,  vertical
hammer mills are believed to have lower wear rates than  horizontal units
and the wear also appears more evenly distributed in the vertical typeJ^J-'
Savagei§' discusses the effect of rotor speed and the  effect of hard fac-
ing alloys on hammer wear. Table ?JL§'  shows the significance of both of
these effects quantitatively and the data  point out, that,  at the lower
speed nonhard faced hammers exhibit greater decrease in  wear. If one had
a choice of either reducing speed or hard  facing the hammer, the former
would be the more viable alternative. If the speed cannot be reduced,  then
hard facing of the hammers is imperative to prolong hammer life. The latter
statement is also supported by the experience at Madison where the hammer
life is increased almost five-fold on the  Gondard mill as a result of hard
facing
                                   30

-------
    Table 7.  AVERAGE WEAR FOR HAMMERS AND GRATE BARS UNDER DIFFERENT
                 SPEEDS AND HAMMER FACING CONDITIONS^/
                                 Average wear, kg/Mg (Ib/ton)
                                   1,200 rpm        790 rpm

Full set of hard faced hammers   0.034 (0.068)   0.024 (0.047)
Full set of nonhard faced
  hammers

Grate bars
0.054 (0.107)   0.031 (0.061)

0.027 (0.053)   0.017 (0.034)
                                Decrease
                                in wear
                                at lower
                                 speed

                                   31%
43%

36%
                                    31

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                               SECTION IV

                           SHREDDER SELECTION
     Generally shredders are selected based on motor horsepower using
known throughputs and required product particle size. Therefore, we have
reorganized data contained in Figure 5 to obtain a graphical relationship
between power requirement (kw) and feed rate (Mg/hr) for different char-
acteristic particle size,  xo  . This relationship is shown in Figure 12.
In deriving this figure, we used values from 0.51 to 5.1 cm (0.2 to 2 in.)
for xo  and their corresponding specific energy consumption values (kw-hr/
Mg) from Figure 5. We then assumed a linear relationship to exist between
power requirement and feed rate. For example, for  XQ = 2.0 cm (0.8 in.),
the specific energy consumption = 16.3 kw-hr/Mg (19.8 HP-hr/ton) from
Figure 5. This translates to 148 kw (198.3 HP) at a feed rate of 9.1 Mg/hr
(10 tons/hr), for  XQ  = 2.0 cm (0.8 in.), and to 296 kw (396.6 HP) at a
feed rate of 18.1 Mg/hr (20 tons/hr) for the same  xo . Since feed rate
and power are assumed to be linearly related this will provide one line
on Figure 12 for  XQ  = 2.0 cm (0.8 in.). Similarly, other lines were ob-
tained for  xo  values ranging from 0.51 to 5.1 cm (0.2 to 2 in.). It
should be noted that the predictions are based on studies using typical
municipal refuse. The actual power requirements would vary according to
the size and nature of the material to be shredded. Reference 2 has re-
ported suggested minimum horsepower for different waste categories and
has;tabulated power-output particle size—throughput relationships for
some installations. Some other criteria involved in shredder selection
are also presented.-?.'
                                   32

-------
                               FEED RATE (Tons/Hr)
                                       10
   5,000 -
   1,000 -*
Z
LLJ
o
LU
UJ
s
Q.
                                                                         10,000
                                                                       -  1,000
                                                                                Q-
                                                                                X
                                                                LLJ
                                                                s
                                                                LLJ
                                                                —
                                                                5
                                                                o
                                                                LLJ
                                                                O
                                                                            100
      10 -
                                                                             10
   Figure  12.
                      10        5                      1
                 FEED RATE (Mg/Hr)
Power requirement as a function of feed rate and characteris-
  tic particle size desired (xo refers to 63.2% cumulative
  passing in a Rosin-Raramler distribution as defined earlier).
                                         33

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                               SECTION V

                             SHREDDER COSTS
     Available cost data are generally presented in different  formats  due
to variations in bookkeeping practices. Therefore,  ambiguities arise when
direct comparisons or specific data are desired. Throughout  this  section
we have attempted to present cost data in a comparable manner  and have
provided the basis for our interpretation of the available information.

     The cost analysis has been broken down into capital, operating, and
maintenance costs. Furthermore, the analysis includes only those  costs
which are directly associated with the shredder operation and  does  not
take into account costs for building,  ground,  light, water,  heat, etc.

CAPITAL COST

     Information on capital costs for  commercially  available shredders is
limited. The problem is enhanced by the fact that costs  provided  by dif-
ferent manufacturers are not readily comparable since some include  acces-
sories such as feed conveyors, hoppers, etc.,  and others do  not.  Also, the
companies do not provide a breakdown for the cost of the accessories.  Some
shredder manufacturers also include the cost of an  extra hammer set as part
of the initial cost. In times of high  inflation, the cost data also depend
upon when the figures were released. Table 8 has attempted to  eliminate
some of these inconsistencies in reporting capital  cost  information for
different types of shredders.

     Table 9 provides capital cost values for shredders  of equivalent  size
and identical accessories. These values were obtained from different manu-
facturers via their quotations for a recent shredder installation.  From
Table 9 the cost per megagram  per hour is seen to  vary  from $3,500 to
$6,200. Assuming an average capital cost of $4,410/Mg/hr ($4,000/ton/hr),
estimated equipment life of 20 years with no salvage value,  an interest
rate of 6% and an operating time of 1,820 hr/year,  the annualized capital
cost was calculated using the following relationship.^'
                                   34

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                        Table 8.  INITIAL COST FOR SHREDDERS OF VARIOUS CAPACITIES
Capacity
Manufacturer Model
Hammermills, Inc.-/ 4260

6060

6080

74104
96104
(Mg/hr)
22

29

36

73
109
(tons/hr)
24

32

40

80
120
Capital
cost ($)
45.00QW
(88,000)£/
80,000k/
(126,000)£/
lOO.OOOi/
(151,000)£/
(207,000)£/
(300,000)£/
Cost per ton
per hour ($)
l,875b/
(3,667)£/
2,500k/
(3,938)£/
2,500.b/
(3,775)£/
(2,588)£/
(2,500)£/
Cost per Mg
per hour ($)
2,067£/
(4,043)=/
2,756i/
(4,342)£/'
2,756i/
(4,162)£/
(2,853)=/
(4,342)£/
American Pulverizer
  Company^'
The Hail CompanyS/
The Carborundum
  Company^'
   4200
   48-50
   60-50
   60-90
   72-72
   72-84
   96-90

   42-D
   42-F
92-(500 HP)
92-(750 HP)
92-(l,000 HP)

   100
   400
   1000
   9
  18
  27
  45
  91
  91
 136

  14
  13
.  45
  54
  68

 1-4
14-32
27-50
  10
  20
  30
  50
 100
 100
 150

  15
  20
  50
  60
  75

 1-4
15-35
30-55
 12,300
 30,000
 25,600
 51,000
153,000
167,000
259,000

 76,000
 86,000
255,000
260,000
267,000

 18,000
 38,000
100,000
1,230
1,500
  853
1,020
1,530
1,670
1,727
5,100
4,300
 ,100
 ,300
 ,560
                                                                                    5,
                                                                                    4,
                                                                                    3,
7.20QS/
1.52QS/
2.352S/
1,356
1,654
  940
1,125
1,687
1,841
1,904

5,623
4,741
5,623
4,741
3,925

7.938S/
1,676£/
2.593S/
a/  Source:  Hammermills, Inc., Bulletin 1972. Prices quoted are for basic shredders  only;  feed  conveyors,
               hoppers, chutes, power, etc., are not included.
W  Standard model.
£/  Compression fedder model.
d/  Source:  American Pulverizer Company, Bulletin R71 and private communication  in November  1975  and  June
               1975 with Mr. Lin Baker.
e_/  Private communication with Mr. Erv Domanski of Heil Company in November  1975  and  June  1976.  The  company
      usually furnishes shredder and the auxiliary systems and costs reported here are  approximated  for
      shredder alone by using 407. of total cost.
_f/  Source:  The Carborundum Company provided total cost of shredder and accessories  such  as  discharge
               chute, infeed hood, motor, and controls. Cost for shredder alone had to  be  computed assum-
               ing 407. of total cost to be applicable to shredder.
£/  Computed with mean capacity.
                                                         35

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       Table 9.   INITIAL COST FOR SHREDDERS OF EQUIVALENT SIZE

Capacity-/
Manufacturer
A
B
C
D
E
F
(Mg/hr)
45
45
45
45
45
45
(tons/hr)
50
50
50
50
50
50
Capital
costk/,
($)
160,000
190,000
210,000
280,000
230,000
280,000
Cost per unit capacity
($/Mg/hr)
3,500
4,200
4,600
6,200
5,100
6,200
($/ton/hr)
3,200
3,800
4,200
5,600
4,600
5,600
al  Capacities for MSW.
t>/  Capital cost includes infeed conveyors, motors, and other acces-
      sories.
                                   36

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                           AC = (P-L) (CRF) - Li

Where   AC = annualized capital cost

         P = initial cost

         L = salvage value

       CRF = capital recovery factor

         i = interest rate.

The computed values are shown in Table 10. It can be seen from Table 10
that the annualized cost per megagram is constant and independent of the
rated capacity. The estimated unit cost (cost/Mg) is compared with those
reported for the Gainesville, Madison and St. Louis  plants  <*'  in Table
11. It is obvious that factors such as assumed equipment life, interest
rate, and machine operating hours affect the unit cost.  Of these, the most
sensitive appears to be the operating time. For example, an increase of
operating time from 5 to 8 hr/day in Madison would have  significantly re-
duced unit costs of the Gondard and Tollemache mills from $1.21 to $0.847
Mg ($1.10 to $0.76/ton) and from $0.49 to $0.31/Mg ($0.44 to $0.28/ton),
respectively. Thus, all of these factors must be considered when compari-
sons are made.

     The addition of a secondary shredder can be guided  by factors such
as ultimate product size desired, amount and extent  of resource material
to be recovered, capital and maintenance costs, etc. However, private com-
munication with industry personnel indicates that the major advantage may
be one of reducing maintenance costs. At this point, we  can only say that
capital costs will increase with multi-stage shredding.  The data base on
hand is inadequate to conclusively determine the benefits of multi-stage
shredding. Such information may become available when the Ames project
gets underway.

     Information on maintenance and operating cost is scarce and even the
available information is not amenable for direct comparison between dif-
ferent systems. Therefore, we have used estimated costs  provided by manu-
facturers and compared them with actually observed values whenever possi
ble. This discussion is contained in the following sections.

MAINTENANCE COSTS

     Maintenance costs reported by manufacturers are generally variable.
Table 12 shows maintenance costs; associated with various parts of two
particular shredders.
                                   37

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                                 Table 10.   ESTIMATED ANNUALIZED CAPITAL COST
OJ
oo
Refuse processed
Capacity per yearS'
(Mg/hr) (tons/hr) (Mg) (tons)
9.07 10 16,500 18,200
45.35 50 82,500 91,000
90.7 100 165,000 182,000
Annual! zed capital Annual! zed capital cost based
costk' based on on refuse processed annually
capacity ($) ($/Mg)
3,487 0.21
17,436 0.21
34,872 0.21
($/ton)
0.19
0.19
0.19
       &l  Assuming single-shift operation with machine running 5 days/week at 7 hr/day and 1 hr of
             general maintenance or cleanup.
       W  Assuming a capital cost of $4,410/Mg/hr (4,000/ton/hr), zero salvage value, equipment life
             of 20 years, and 6% interest rate.

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                      Table 11.   COMPARISON OF UNIT COSTS  FOR MADISON AND GAINESVILLE PLANTS
-UJ
 VD
                          Estimates based
                            on Table 10
Unit cost

  $/Mg

  $/ton
                               0.21

                               0.19
                                             Madison,  Wisconsin,
                                            	plant	
                                      Gondard
                                        Mill
      .Shredder capacity

        Mg/hr             9.1,  45 and 91    7.3

        tons/hr           10,  50 and 100    8
           Tollemache
              Mill
                                                 14

                                                 15
Gainesville, Florida,
       plant
(Williams Hammermill)
Primary     Secondary
  unit         unit
                        27
                        30
             18
             20
i  ina,b/    n 443,c/
St. Louis refuse
processing plant
   (Gruendler
    60 x 84)
    45

    50
      a./  Costs include conveyors.
      W  Computation based on $4,000 salvage value,  equipment life  of  15  years,  5.8% interest,  and 5.5
            hr/day (for June 1968-May 1969).
      £/  Computation based on $4,000 salvage value,  equipment life  of  15  years,  5.9% interest,  and 5.3
            hr/day (for July 6-October 9,  1970).
      cl/  Costs include motor, starter, extra hammer set,  transportation,  structural  support,  installa-
            tion,  and consultants.  Amortization based on effective interest  rate  of 6% over 10-year
            period.  Machine operating time was 8 to 10 hr/day (for July-October 1969).
      £/  Costs include motor. Amortization based on interest rate of 6% and  20 years  capital recovery.
            Values are for October  1974-September 1975.  Monthly average ranges from $0.15 to $2.17/Mg
            ($0.14 to $1.97/ton).   Source:  Midwest Research Institute, Final Draft Report to EPA on
            Contract No.  68-02-1324 and Contract No.  68-02-1871, March  19,  1976).

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                    Table 12.  MAINTENANCE COST FOR VARIOUS COMPONENTS OF TWO SHREDDER UNITS
   Manufacturer

Hammermills, Inc.£'
Gruendler Crusher^'
  and Pulverizer
  Company
                                   Estimated maintenance cost,  $/Mg ($/ton)
Part
Hammers
Cutter bar
Material
0.14 (0.13)
0.08 (0.07)
Labor
0.03 (0.03)£/
0.07 (0.06)£/
Total§/
0.32 (0.2
Hammers

Side liner

Grate

Pin

Top anvil

Breaker plates
0.103 (0.093)

0.0326 (0.0296)

0.0841 (0.0763)

0.012 (0.011)

0.017 (0.015)

0.017 (0.015)
0.120 (0.109)£/

0.0018 (0.0016).§/

0.0009 (0.0008)£/



0.0008 (0.0007)^

0.0008 (0.0007)^
                                                                           0.39 (0.35)
   Other information

Model 6080 shredder with
  force feed, reversible
  hammers, requires no
  tipping, nominal prod-
  uct size 7.6 cm  (3  in.)

Model 60X84 shredder, re-
  versible hammer, prod-
  uct size 10-15 cm
  (4-6 in.)
&l  Total cost does not include electric power used for maintenance.
t>/  Company estimates based on figures from the City of Harrisburg,  Pennsylvania.
£/  Labor cost computed at $15/hr.
_d/  Manufacturer estimates for City of Omaha, Nebraska.
o_l  Labor cost computed at $10/hr.

-------
Hammermills, Inc., released only maintenance cost for hammers and cutter
bar. A more detailed breakdown on the maintenance expenses was given by
Gruendler Crusher and Pulverizer Company. The total cost of maintenance
reported in Table 12 does not include costs for minor maintenance on bear-
ings, seals, motors, etc., nor replacement of shaft and rotor. However,
data shown in Table 13 include maintenance costs for motors, feed convey-
ors, and other accessories and are thus higher than those in Table 12.
Values contained in Table 13 were estimated by the manufacturers. Because
of the lack of field data on these specific shredders we have not been
able to compare manufacturers' maintenance data with those actually ex-
perienced.             .             .

     Maintenance costs observed at Madison and Gainesville shredders are
shown in Table 14_iP-iI2'  Even though manufacturer supplied maintenance
data are not available,for comparison, we have included them to provide
an indication of costs actually experienced. In each case, the cost can
be reduced by proper maintenance such as frequent examination of hammers
and associated components, and hard facing and tipping. In Madison,  such
procedures resulted in a savings of 25£/Mg (23^/ton) processed*i2'

     When a secondary unit is used, the maintenance cost for both units
together is claimed to be lower than when one unit alone is operating to
achieve the required product size. However, this claim has not been docu-
mented.

OPERATING COST

     Operating costs have been computed for three different capacities,
9.1, 45, and 91 Mg/hr (10, 50, and 100 tons/hr) based on the following
assumptions.

     1.  Single shift operation for 5 days/week at 7 hr/day for produc-
tion, and 1 hr/day for general maintenance and cleanup.

     2.  One man working full time and another working halftime are used
for operating the shredder and for general maintenance at $7.00/man-hour.

     3.  Typical value of 20.6 kw-hr/Mg (25 HP-hr/ton) for MSW is used  for
computing energy cost.

     4.  Power cost is $0.02/kw-hr (even though this is generally varia-
ble, we believe that this rate would be a good overall average rate).

     The operating costs for plant capacities of 9.1,  45,  and 91 Mg/hr  (10,
50, and 100 tons/hr) are shown in Table 15.
                                   41

-------
              Table 13.  MAINTENANCE COST FOR (45 Mg/hr) SHREDDER UNITS AS PROVIDED BY MANUFACTURERS^/
to
                                  Estimated maintenance cost,
                                  	$/Mg ($/ton)	
        Manufacturer
 Material
     Pennsylvania Crusher    0.25 (0.23)   0.12 (0.11)
       Corporation

     Carborundum Company     0.35 (0.32)   0.09 (0.08)
     American Pulverizer     0.20  (0.18)   0.42 (0.38)
       Company
      Heil Company
0.61 (0.55)   0.11 (0.10)
      Jeffrey Manufacturing   0.62 (0.56)   0.18 (0.16)
        Company

      Gruendler Crusher and   0.47 (0.43)   0.35 (0.32)
        Pulverizer Company
  Total£/

0.37 (0.34)


0.44 (0.40)


0.62 (0.56)


0.72 (0.65)


0.79 (0.72)


0.83 (0.75)
          Other information

Model BW-6080, horizontal shaft design,
  746 kw (1,000 HP)

Model 1000, vertical shaft design, 373
  kw (500 HP)

Model 60X90, horiziontal shaft design,
  reversible rotor, 746 kw (1,000 HP)

Model 92-A, vertical shaft design, re-
  versible hammer, 373 kw (500 HP)

Model 990, horizontal shaft design,
  746 kw (1,000 HP)

Model 60X84, horizontal shaft design,
  reversible hammer, 746 kw  (1,000 HP)
      aj  For  typical product size of 10-15 cm  (4-6 in.).
      W  Labor cost computed at $15/hr.
      c/  Total cost includes maintenance for feed conveyors, motors, and other accessories.

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                 Table 14.  MAINTENANCE COSTS OBSERVED AT MADISONI2/ AND GAINESVILLfili/
                                                   Maintenance cost, $/Mg  ($/ton)
      Grinder

Gondard Mill
(Madison, 1969)£/

Tollemache Mill
(Madison, 1969 )^/
Williams Hammermill
(Gainesville, 1969 -
primary unit)
  •  ~ ••••
Williams Hammermill
(Gainesville, 1969 -
secondary unit)
      Part

Hammer wear
Mill maintenance

Hammer and shaft
Welding rod
Mill maintenance

Hammer build-up
Maintenance and
  repairs

Hammer build-up
Maintenance and
  repairs
   Material

0.17 (0.15)
0.20 (0.18)£/

0.151 (0.137)
0.036 (0.033)
0.074 (0.067)£/

0.093 (0.084)
0.359 (0.326)
0.040 (0.036)
0.466 (0.423)
     Labor
0.46 (
0.57 (0.52)W
0.36
                                                            0.45
0.157 (0.142)!/
0.195 (0.177)!/
    Power           Total
                1.40  (1.27)
                1.077  (0.977)
0.300 (0.027)   0.834  (0.756)
0.265 (0.240)f/   0.031 (0.028)
0.100 (0.091)J!/
                1.012  (0.918)
al  Cost data are for operation with grate size of 12.7 cm  (5 in.), June 1968-May  1969.
b_/  During a different test period in Madison, labor costs  for hammer and repair maintenance were  12 and
      15% of total  labor cost. These values are used in computing the labor cost here.
£/  Material cost includes those for mill maintenance and general supplies.
d/  Cost data are for test period July 6-October 9, 1970.
£/  Plant supplies  and replacement parts.
^/  Labor cost includes fringe benefits.

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                       Table 15.   ESTIMATED OPERATING  COST FOR PRIMARY SHREDDER UNITS
Capacity
(Mg/hr) (tons/hr)
9.1 10
45 50
91 100
Refuse
processed
per yearii'
(Mg) (tons)
16,500 18,200
82,500 91,000
165,000 182,000
Power Ji/
Annual
($)
6,825
34,125
68,250
Cost Cost
Mg ton
f
-------
Based on present assumptions, power cost per megagram remains the same
for any capacity while labor cost per megagram decreases with capacity.
Figure 13 shows the operating costs for various capacities obtained
from Table 15. The operating cost decreases with increase in capacity
and is asymptotic at about 91 Mg/hr (100 tons/hr). The figure also
shows the operating cost observed at the Madison and Gainesville shred-
ding facilities*i2il2'  Differences in operating cost can be caused by
variations in operating capacity, power consumption (due to variations
in shredder design), labor wage rates, number of operators employed,  etc*
Therefore, the differences observed are not highly significant.

     The operating cost for a secondary unit is expected to be slightly
lower than that of the primary unit due to reduced power consumption  as
a result of smaller and more uniform input material. This expectation is
observed in Figure 13 for the Gainesville secondary unit. Also, air clas-
sification systems following the primary unit would help reduce the amount
of heavier input material and hence conserve energy.

COMBINED COST                           :

     The combined cost of shredding MSW has been estimated using the  cap-
ital, maintenance, and operating costs (discussed above). This cost is
tabulated in Table 16 and shown in Figure 14. On a per-megagram basis,
the maintenance and operating costs are the dominant factors. Figure  14
also compares the estimated combined cost with actual costs observed  at
the Gainesville, Madison, and St. Louis plants. The Gainesville facility
is a two-stage operation and the combined cost for each stage was obtained
from Ref. 19. The St. Louis cost data are reported for the entire process-
ing plant including the shredder, air density separator, magnetic separa-
tor, nuggetizer, etc.,  and we have not been able to identify shredder costs
separately. Therefore,  the St. Louis costs are higher than those estimated.
The Madison costs are also higher than the estimated costs. This is proba-
bly because it was one of the earliest facilities to go into operation.

     The estimated cost curve in Figure 14 shows a minimum at about 68 Mg/
hr (75 tons/hr) rated capacity. Even though this may not be the exact opti-
mum capacity for a new facility, it certainly indicates that one should
seek an optimum value in designing or selecting a shredder.
                                   45

-------
      0
           20
   2.4
   2.0
   1.6
O
u
O
Z 1.2
UJ
Q_
O
   0.8
   0.4
_$3.12/Mg

       L  D   A
      0
                  0
RATED CAPACITY (Tons/Hr)
     40          60          80
                      D  Gondard Mill, Madison 15/
                      A  Tollemache Mill, Madison M
                      O  Williams Shredder,  Gainesville  12
                             ( Primary)
                      0  Williams Shredder, Gainesvillel^
                             (Secondary )
                            •Estimated Operating Cost
                             (From Table 15)
                                  I
                                        I
            20            40            60
                  RATED CAPACITY (Mg/Hr)
80
       100

         2.4
                                                              2.0
                                                                      1.6   o
              I/O
              O
              u
         1.2
               .
              LU
              O.
              O
                                                                     0.8
                                                                     0.4
                                          90
Figure 13.  Estimated  operating cost for various shredder capacities.
                                    46

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                           Table 16.  COMBINED COST OF SHREDDING MSW

Capital
Capacity cost^'
(Mg/hr)
9.1
45
91
(tons/hr) ($/Mg)
10 0.21
50 0.21
100 0.21
($/ton)
0.19
0.19
0.19
Maintenance
($/Mg)
0.33
0.55
0.77
($/ton)
0.30
0.50
0.70
Operating
($/Mg)
1.74
0.68
0.55
($/ton)
1.58
0.62
0.50
Combined cost
($/Mg)
2.28
1.44
1.53
($/ton)
2.07
1.31
1.39
a/  From Table 10.
b_/  Estimate based on private communication with manufacturers.
c/  From Table 15.

-------
-o
 0)
 
                    i/i
                    irt
                    V
                    O
                    O
                    §
                    u-
                    0)
                                                                          c
                                                                          O

                                                                         O
                                                                         u
                                                                              O
      .0
                                                                         1.0
      0
                                     I
                      20            40            60
                             RATED CAPACITY, Mg/hr
                                                           80
             Figure 14.  Total cost versus rated capacity.
                                         48

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                                SECTION VI

             EVALUATION OF MATERIAL/ENERGY RECOVERY SYSTEMS
     We have evaluated material/energy recovery systems such as  pyrolysis
and combined firing (coal-refuse) to determine the cost and performance
benefits resulting from shredding refuse to finer levels.  The specific
processes that were studied are shown in Table 17. In addition,  we have
contacted operators of these systems to obtain information on process con-
straints which dictate the need for shredding, the maximum particle size
the system can tolerate, and performance improvements that result from
finer particles. Cost benefits which might accrue due to enhanced material
recovery or performance were also sought. The available information is  sum-
marized below. It should be noted that the emphasis is on the shredding
aspects of these systems.
     Table 17.  PYROLYSIS AND COMBINED FIRING SYSTEMS INVESTIGATED
              TO DETERMINE THE BENEFITS OF FINE SHREDDING
     Pyrolysis

     •  Monsanto Landgard system
     •  Union Carbide Purox process
     •  Occidental Petroleum Garrett process
     •  Battelle Northwest pyrolysis system
     •  West Virginia University pyrolysis process

     Combined firing

     •  Homer-Shifrin supplementary fuel process (St.  Louis,  Ames)


PYROLYSIS SYSTEMS

     In the Monsanto Landgard system, which is operational at  Baltimore,
mixed municipal solid waste is shredded to approximately 10.2  cm (4  in.)
                                   49

-------
in one of two 45 Mg/hr (50 tons/hr) shredders. It is then fed into  a re-
fractory lined rotary kiln which acts as the pyrolyzer.  No additional
information is available on the shredding aspects to permit an evaluation
of cost/performance benefits of this system.

     The Linde Division of Union Carbide Corporation has developed  a high
temperature pyrolysis system, called the Purox system, which utilizes
nearly pure oxygen for the combustion of pyrolysis char. The main advant-
age of using pure oxygen is that the pyrolysis gas is -free of nitrogen.
The Purox system originally did not utilize shredded refuse as feed into
the pyrolysis reactor but recently the refuse is being shredded to  a typi-
cal size of 15.2 cm (6 in.). It is claimed^0-' that the maximum particle
size the system can tolerate is 22.9 cm (9 in.) and that the system is
guaranteed only for shredded refuse. No other data are currently avail-
able to us.

     Occidental Petroleum's Garrett pyrolysis process is a "flash"  pyrol-
ysis process which requires most nonorganic material to  be removed  from
the refuse feed. The process also requires the organic material to  be re-
duced to small, dry particles. Therefore, the feed (MSW) is first shredded
to a particle size of 7.6 to 10.2 cm (3 to 4 in.) in a primary shredder*^/
It is then air classified to separate the light, organic fraction from the
heavy, inorganic fraction. The lights are then dried to  a moisture  content
of 3%. A screen is used to remove additional inorganics  and the remaining
material is again shredded to a particle size of -20 to  -30 mesh*^='

     Table 18 shows a typical size distribution of prepared refuse  for
the Garrett process*^' It is claimed that the system will not work  with-
out secondary shredding due to the very short residence  time in the reac-
tor.^'  Cost data on the system are not available to us.

     Battelle Northwest has conducted experiments in a vertical shaft
pyrolysis reactor with shredded, unsegregated refuse at  a feed rate of
about 81.6 kg/hr (180 Ib/hr). The size of refuse is about 30.5 cm (12 in.)
across and it is believed that fine shredding of the refuse will plug up
the reactor bed and hamper the processJL?'

     The West Virginia University pyrolysis process makes use of two
fluidized beds; one for pyrolysis and another for combustion. The refuse
entering the pyrolysis (fluidized bed) reactor is shredded, classified,
and dried. Initial experiments demonstrated the need for preprocessing
raw refuse. The Stanford Research Institute studyA-i' recommended a  maxi-
mum particle size of 2.5 cm (1 in.) but systematic investigations relat-
ing effect of particle size or performance/cost benefits have not yet
been undertaken*^'
                                   50

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 Table 18.  SIZE DISTRIBUTION OF GARRETT SECONDARY SHREDDED
            SOLID WASTE!/ (ORGANIC PORTION ONLY)
              Size
Tyler mesh
  (in.)                  Microns               Wt.  % retained

   1/4                    6,350                      6.0
    16                      991                     21.0
    20                      833                      3.9
    32                      495                     19.1
    48       .               295                     11.7
    80                      175                      9.1
   100                      147                      4.8
   150                      104                      4.6
   200                       74                      4.9
  -200                      -74                     14.9
Note:  Solid waste ground to this size is of a matted,  fibrous
         nature. Screen size is not an accurate measure of par-
         ticle length or width particularly above 20 mesh where
         considerable "balling" is apparent.
                              51

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COMBINED FIRING SYSTEMS

     The Horner-Shifrin process is used in the St. Louis project.-^'
This project is demonstrating the feasibility of using processed munici-
pal refuse as a supplementary fuel with coal in a power plant boiler. The
raw municipal solid waste goes through a hammermill where it is reduced
to less than 6.35 cm (2.5 in.) in size. It is then passed through an air
classifier which separates it into a light fraction and a heavy fraction.
From the heavy fraction, ferrous metals are recovered using a magnetic
drum and the nonmagnetic metals and glass go to a landfill. The light
fraction is used as the supplemental fuel for the power plant boiler.
Table 19 shows the typical size distribution for the shredded, air clas-
sified refuse. Cost data are reported for the entire processing plant and
we have not been able to identify shredder costs independently. The same
difficulty was also encountered in evaluating the shredder performance in-
dependent of other systems at the processing facility. Union Electric en-
gineers claim that fine shredding of refuse does result in better heat re-
covery. They interpret a higher heat recovery with refuse ground to less  than
3.18 cm (1.25 in.) when compared to refuse less than 7.6,cm (3 in.) in size
                                                      o c /
based upon megawatts generated per megagram of refuse.—  The St. Louis study,
however, reports that the combustion efficiency did not improve with fine
ground refuse when based on the two data points for fine-ground refuse.—'
            Table  19.  TYPICAL SIZE DISTRIBUTION OF SHREDDED,
                  AIR CLASSIFIED REFUSE IN ST. LOUIsift/
                  Size

    Percent  larger than 6.4 cm  (2.5 in.)                          2.5
    Percent  less than 6.4 cm  (2.5 in.)                           97.5
    Percent  less than 3.8 cm  (1.5 in.)                           94.0
    Percent  less than 1.9 cm  (0.75 in.)                          73.5
    Percent  less than 0.95 cm (0.375 in.)                        49.0
    Percent  less than 0.47 cm (0.187 in.)                        31.9
    Percent  less than 0.24 cm (0.094 in.)                        21.2
     The Ames project which is expected to commence shortly will be ad-
dressing many of the aspects that could not be covered in the St. Louis
study. For instance, it will be the first operating refuse shredding/firing
facility to use magnetic separation between two 45 Mg/hr (50 tons/hr)  shred-
ders and an air classifier following the second shredder. Such a setup
                                   52

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should provide field data on the benefits of two-stage shredding,  varia-
tions in energy consumption between the two stages and variations  in main-
tenance and operating costs. Much of these data are presently  unavailable.

SUMMABY

     Our review of the available information and our conversations with
operators of material/energy recovery systems indicate that process con-
straints primarily dictate the need for shredding refuse.  It is  logical
to assume that fine shredding will enhance energy recovery by  improving
the combustion/thermal reaction efficiency. Also, material recovery should
improve with fine shredding particularly in air separators. However, field
test data documenting these aspects are currently not available. The inclu-
sion of fine shredding capability in the overall system,  to reduce the
product size distribution, will increase capital costs, but in the long
run, the system's enhanced performance both in terms of energy recovery
and in terms of material recovery may help offset this additional  cost.
In fluidized bed systems, however, the need for fine shredding has to be
critically evaluated in conjunction with bed characteristics.  At present
the available data are insufficient to make any definite  conclusions.
                                   53

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                               SECTION VII

                     CONCLUSIONS AND RECOMMENDATIONS
     Most of the reported field data on shredders including performance
and costs are related to the Madison, Gainesville,  and St. Louis studies.
Our discussion has been based on these studies as well as those of Trezek
at the University of California, Berkeley.

     Several factors affect shredder performance and these include feed
moisture content, shaft speed, grate spacing, feed composition, and par-
ticle size distribution. Of these, the effects of feed composition and
feed particle size distribution on the specific energy consumption and
product size distribution are not well characterized. Also, all of these
factors should be studied on field units and under field conditions.

     Cost data are available for specific shredder installations, but due
to different bookkeeping systems, we have found it difficult to compare
costs directly. Our estimates indicate that the capital cost is about
$4,410/Mg/hr ($4,000/ton/hr), and the annualized unit cost (excluding op-
erating and maintenance costs) is $0.21/Mg ($0.19/ton). Maintenance and
operating costs were estimated to be about $0.33 and $1.74/Mg ($0.3 and
$1.58/ton), respectively, for a throughput of 9.1 Mg/hr (10 tons/hr); for
a throughput of 91 Mg/hr (100 tons/hr), they were about $0.77/Mg ($0.7/ton)
for maintenance costs and $0.55/Mg ($0.5/ton) for operating costs. All of
these costs, however, should be used with caution.

     Evaluation of material/energy recovery processes such as pyrolysis
and combined firing systems indicates the apparent lack of quantitative
information on the cost/performance benefits of fine shredding in such
systems. We feel that process constraints dictate the need for shredding
in such processes.

     Based on the above observations, it is recommended that tests be con-
ducted in the field to systematically characterize the effect of variables
affecting shredder performance. These tests are critical to optimize shred-
der performance and to establish design criteria for obtaining required
product size distribution and throughput. During these tests, the perform-
ance of the overall material/energy recovery process should also be
                                   54

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systematically studied to establish the optimum particle  size  required
and to evaluate the benefits of fine shredding  in such  systems.  In  con-
junction with these tests, it is imperative that cost data  also  be  col-
lected in a systematic, standardized manner throughout  the  process  to (a)
determine operating and maintenance costs,  and  (b)  evaluate cost benefits,
if any, that may arise from shredding refuse to finer levels in  material/
energy recovery processes.

     Projects utilizing municipal solid waste either as supplemental fuel
or as principal fuel are underway at Ames and Baltimore,  respectively.. As
discussed earlier,  both of these processes  require  the  refuse  to be shred-
ded prior to combustion/pyrolysis. Also, the University of  California at
Berkeley is currently involved in a fine shredding  study. It is  therefore
recommended that these studies incorporate  performance/cost evaluation of
the overall system, including shredding operations, along the  lines out-
lined above. Future projects should acquire such data,  as part of the over-
all effort, in order to provide an adequate data base for any  type  of
definitive analysis.
                                   55

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                               REFERENCES
 1.  "Inventory of Municipal Solid Waste Size Reduction Equipment," pre-
       pared by Midwest Research Institute for EPA under Contract No,  68-
       03-0137, June 1973.

 2.  "Solid Waste Shredding and Shredder Selection," EPA Publication No.
       EPA/530/SW-140, March 1975.

 3o  "Energy Recovery from Solid Waste," Vol. II,  NASA-ASEE 1974 Systems
       Design Institute NASA Grant NGT-44-005-114, September 1974.

 4o  Trezek, G. J., "Size Reduction Equipment." Compost Science, pp. 22-
       25, September/October 1973.

 5o  Private communication with Mr. H.  D. Funk of  Henningson,  Durham,  and
       Richardson, Omaha, Nebraska*

 60  "Combined Firing Applications Study," prepared by Midwest Research
       Institute under EPA Contract No. 68-02-1324, Task 20, December  1974.

 70  Waste Age, pp. 10-15, July 1975.

 80  Ruf, J. A., "Particle Size Spectrum and Compressibility of Raw and
       Shredded Municipal Solid Waste," Ph.D. Thesis,  University of
       Florida, 1974.

 9.  Gawalpanchi, R. R., P. M.  Berthouex, and R. K. Ham, "Particle Size
       Distribution of Milled Refuse,"  Waste Age,  pp.  34-74, September/
       October 1973.

10.  Reinhardt, J. J., and R. K. Ham, Final Report on a Demonstration
       Project at Madison, Wisconsin, to Investigate Milling of Solid
       Wastes, Vol. I, 1966-1972, EPA Office of SWMP,  March 1973.
                                   56

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11.  Trezek, G. J., D. M. Obeng,  and G.  Savage,  "Size Reduction in Solid
       Waste Processing," 2nd Year Progress Report 1972-1973,  College of
       Engineering, University of California,  Berkeley.

12.  Trezek, G. J., and G. Savage, "Results of a Comprehensive Refuse
       Comminution Study," Waste  Age, pp.  49-55, July 1975.

13.  Obeng, D. M., and G. J.  Trezek, "Simulation of the  Communition of a
       Heterogeneous Mixture  of Brittle  and Nonbrittle Material in a Swing
       Hammermill," Ind. Eng. Chem. Process Des. Dev., 14(2):113,  1975.

14.  Shannon, L. J., D. E. Fiscus, and P.  G. Gorman,  "St.  Louis Refuse
       Processing Plant:  Equipment, Facility  and Environmental Evalua-
       tions," EPA Publication No. EPA-650/2-75-044,  May 1975.

15.  "Solid Waste Reduction/Salvage Plant," 3rd Progress Report,  City of
       Madison Pilot Plant, June  14, 1967  through December 28, 1968, pre-
       pared by project personnel at Madison,  Wisconsin, for the U.S.
       Public Health Service, Bureau of  Solid  Waste Management, 1969.

16.  Private communication with Dr. G. J.  Trezek,  University of California,
       Berkeley, December 12, 1975.

17.  "Development of a Standardized Procedure  for the Evaluation and Com-
       parison of Size Reduction  Equipment," Final Report, prepared by
       Midwest Research Institute for EPA  under Contract No. 68-03-0137,
       January 23, 1973.

18.  Savage, G., and G. J. Trezek, "On Grinder Wear in Refuse  Communition,"
       Compost Science-Journal of Waste  Recycling,  15(4),  September-October
       1974.

19.  Ruf,  J. A., "Refuse Shredders." Waste Ag;e,  pp. 58-66, May/June 1974.

20.  Private communication with Mr. J. Rivero, Union  Carbide Corporation,
       Tonawanda, New York, December 10, 1975.

21.  Private communication with Mr. Clem Finney, Occidental  Petroleum Cor-
       poration, San Diego, California,  December 10,  1975.

22.  Private communication with Dr. Lyle Mudge,  Battelle Northwest,
       Richland, Washington,  October 17, 1975.

23.  "Pyrolysis of Solid Waste:   A Technical and Economic  Assessment,"
       Stanford Research Institute Report  for  West Virginia  University,
       September 1972.
                                   57

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24.  Private communication with Dr.  Richard Bailie,  University of West
       Virginia,  Morgantown,  October 31,  1975.

25.  Private communication between Mr.  Doug Fiscus of Midwest Research In-
       stitute and Mr.  John Molitar  of  Union Electric, St.  Louis,  January
       7, 1975.

26.  Fiscus, D. E. et al., "Bottom Ash  Generation in a Coal-Fired Power
       Plant When Refuse-Derived Supplementary  Fuel  is Used," presented
       at the ASME Solid Waste Processing Conference,  Boston,  Massachusetts,
       May 23-26, 1976.
                                   58

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                                 TECHNICAL REPORT DATA
                          (Please read Iiiaruc lions on the reverse before completing)
 1. REPORT NO.
  EPA-600/2-76-208
                            2.
                                                      3. RECIPIENT'S ACCESSION NO.
 4. TITLE AND SUBTITLE
 Fine Shredding of Municipal Solid Waste
                                                      5. REPORT DATE
                                                        July 1976
                                                       6. PERFORMING ORGANIZATION CODE
 7. AUTHOR(S)

 K. P. Ananth and J. Shum
                                                      8. PERFORMING ORGANIZATION REPORT NO
 9. PERFORMING OR9ANIZATION NAME AND ADDRESS
 Midwest Research Institute
 425 Volker Boulevard
 Kansas  City, Missouri  64110
                                                       10. PROGRAM ELEMENT NO.
                                                      EHB533
                                                      11. CONTRACT/GRANT NO.

                                                      68-02-1324, Task 39
 12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC  27711
                                                      13. TYPE OF REPORT AND PERIOD COVERED
                                                      Task Final; 6/75-6/76
                                                      14. SPONSORING AGENCY CODE
                                                       EPA-ORD
 is.SUPPLEMENTARY NOTES Task officer for this report is J.D. Kilgros, Mail Drop 61,
 Ext 2851.
 16. ABSTRACT rj,ne repOrt gives an overview of equipment used for municipal solid waste
 (MSW) size reduction and discusses its  performance and cost.  Of the 11 basic equip-
 ment types used for shredding MSW,  only hammermills and grinders find wide appli-
 cation.  An evaluation of available hammermill and grinder performance data indi-
 cates that: their specific energy consumption is independent of throughput for the same
 product size distributions and feed characteristics (power,  however, is a function of
 throughput); higher shaft speeds produce finer  size distributions and require more
 energy for the same throughputs; smaller grate spacings (exit clearances) produce
 finer particles; and for  constant feed and shredder operating conditions,  specific
 energy consumption is a minimum at 30-40% refuse moisture content. On the basis o
 available cost estimates, the initial cost for shredders ranges from $3528 to $6174
 per Mg/hr. Maintenance and operating  costs are estimated to be $0. 77/Mg and $0. 55/
 Mg,  respectively, for shredders of 90.7 Mg/hr capacity. Fine shredding performance
 or cost benefits information is not available. The need for fine shredding in most
 material/energy recovery systems is currently dictated by process constraints and
 the benefits may be system specific.  Generally, fine shredding is expected to enhance
 both energy recovery (by improving combustion efficiency) and material recovery (by
 increased separation effectiveness).  These benefits have not been documented yet.
                             KE'V woHPg AN5 DOCUMENT ANALVSIS
                 DESCRIPTORS
                                         b.IDENTIFIERS/OPEN ENDED TERMS  C. COSATI Field/Group
 Air Pollution
 Fuels
 Wastes
 Shredding
                                          Air Pollution Control
                                          Stationary Sources
                                          Waste as Fuel
                                          Municipal Solid Waste
13B
21D

13H,07A
                                          19. SECURITY CLASS (This Report)
                                          Unclassified
3. DISTRIBUTION STATEMENT

Unlimited
                                          20. SECURITY CLASS (This page)
                                           Unclassified
21. NO. OF PAGES

   59	
                                                                   22. PRICE
EPA Form 2220-1 (9-73)
                                         59

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