resource recovery plant implementation
                guides for
           municipal officials
           • planning and overview
            •technologies • risks
           and contracts • markets
            • accounting format •
           financing • procurement
            • further assistance!

     This publication is part of a special series of reports prepared
by the U.S. Environmental Protection Agency's Office of Solid Waste
Management Programs.  These reports are designed to assist municipal
officials in the planning and implementation of processing plants to
recover resources from mixed municipal solid waste.

     The title of this series is Resource Recovery Plant Implementation:
Guides for Municipal Officials.  The parts of the series are as follows:

     1.  Planning and Overview (SW-157.1)
     2.  Technologies (SW-157.2)
     3.  Markets (SW-157.3)
     4.  Financing  (SW-157.4)
     5.  Procurement (SW-157.5)
     6.  Accounting Format (SW-157.6)
     7.  Risks and Contracts (SW-157.7)
     8.  Further Assistance (SW-157.8)
     Mention of commercial products does not constitute endorsement by
the U.S. Government.  Editing and technical content of this report were
the responsibilities of the Resource Recovery Division of the Office of
Solid Waste Management Programs.

     Single copies of this publication are available from Solid Waste
Information, U.S. Environmental Protection Agency, Cincinnati, Ohio

          Resource Recovery Plant Implementation:

              Guides for Municipal Officials

            This guide (SW-157.2) was compiled
           by Steven J. Levy and H. Gregor Rigo
  Acknowledgements are made to Robert Lowe for chapter II
of this report, and to Robert Holloway, David Sussman, and
     Ivonne Garbe for contributions to other chapters.



SECTION                                                   PAGE

   I.   INTRODUCTION AND OVERVIEW                            1

         Overview                                           1
         Energy Recovery Systems                            3
         Material Recovery Systems                          9
         Conclusions                                       11

         RECOVERY SYSTEM DESIGN                            13

         Markets for Recovered Products                    13
         Waste Generation (Quantity)                        14
         Waste Composition            i                     15
         System Reliability                                16
         Plant Location                                    17
         Land Required for the Plant  Site                  17
         Community Acceptance                              17
         Plant Costs and Revenues                          18

 III.   ENERGY RECOVERY SYSTEMS                             21

         Energy Balances                                   21
         Waterwall Combustion Systems—Unprocessed Waste   22
         Waterwall Combustion Systems—Processed Waste     28
         Solid Refuse Derived Fuel Systems                 29
         Pyrolysis Systems                                 41
         Biological Gasification Systems                   55
         Waste-fired Gas Turbine Systems                   58

  IV.   MATERIALS RECOVERY SYSTEMS                          62

         Paper Fiber Recovery                              62
         Composting                                        67
         Ferrous Metals Recovery                           68
         Glass and Aluminum Recovery  Systems               70

   V.   READING LIST                                        79

                       GUIDE FOR MUNICIPAL OFFICIALS

by Steven J. Levy* and H. Gregor Rigo+

                                 SECTION I

                          INTRODUCTION AND OVERVIEW

     The recent emergence of techniques for converting mixed municipal
waste into marketable products has given municipal and regional
officials a variety of new options for solving their solid waste
management problems.  Although these resource recovery systems cannot
be expected to operate at a profit, they are becoming increasingly
competitive with the cost of sanitary landfill ing in many areas of
the country.  In addition, although they will not allow a community
to close down its landfill, the life of the landfill can be extended
tremendously by the weight and volume reductions achieved.

     The purpose of this technology review is to aquaint the reader
with the available and emerging technology options for processing
of mixed municipal waste for resource recovery.

     Although this report focuses only on mixed waste processing
systems to recover materials' and energy, it is important to remember
that other strategies should also be considered and integrated with
such plants for a complete resource recovery and conservation
strategy.  This includes particularly examination of waste reduction
and source separation strategies.  Fortunately such strategies will
usually be found to be compatible, which allows cities to maximize
recovery and minimize both waste and cost.

     For each technology presented in this report the following
information is presented:
     *Mr. Levy is Manager of the Demonstration and Evaluation Program
of the Resource Recovery Division, Office of Solid Waste Management
Programs, U.S. Environmental Protection Agency.

     +Dr. Rigo is the Principal Engineer for Systems Technology
Corporation, Dayton, Ohio.

        Process description
     .   Product characteristics
        Status of development
        Energy balance

This information should help officials to determine if systems may be
available to meet their needs; and will  help them understand the
technical capabilities and risks associated with various technologies.

     This guide will not tell the reader which system, if any, to
select.  There is no universally "best"  or most economical recovery
technology.  Every community facing a resource recovery decision must
consider its own unique set of factors when selecting a course of
action.  Factors include available markets and local  prices, capital
and operating cost projections, level of risk which they are willing
to assume*, and financing and management alternatives available
for different systems or considerations.

     Unfortunately, goals often conflict, making a choice more
difficult.  For example, the recovery system with the lowest projected
net cost may involve the highest degree  of technological uncertainty.
Or, the system producing products which  can be most readily marketed
through firm contracts may have the highest projected costs.  The
final decision is subject to specific value judgements which each
community must make on its own.  This should normally be done with
the assistance of knowledgeable consultants who can examine in
detail  the feasibility of alternative options, including factors
such as marketing, management, and financing.

     The most important factor to remember when assessing a technology
is that the system must be able to produce marketable products.
Technology selections should not be made until potential markets
have been identified and the market requirements specified.  Some
communities will find that there is only one technical approach that
can simultaneously meet their needs and  the requirements of their
markets.  Most cities, however, will, have the flexibility to choose
from two or more technologies that meet  their market requirements.
the Markets guide of this series (SW-157.3) discusses markets in


     To give communities a better idea of the developmental status of various
technologies, the systems described in this report have been classified
into general categories which are defined below.  Because resource
recovery systems are rapidly evolving, the categorization serves
only as a general guide rather than providing a precise definition
     *Risk is a function of the total dollar investment and the degree
of uncertainty that exists.  Factors subject to uncertainty include
availability of waste, reliability and performance of equipment,
product quality, and market demand.

of status of development.  Primarily, it indicates the degree and scale
of operating experience.  It is important that the decision maker
realize that while the degree of operating experience is one detriment
of the technological risk inherent in recovery systems, another factor,
which may be more important, is the performance guarantee that a system
vender may supply.  Thus, in a particular situation, a system with an
operating history, which is improperly designed or is secured by
no performance guarantees, may entail more risk for a city than a
newer technology designed and properly warranteed by a qualified vender.

     .  Commercially Operational Technology

        Full scale commercial plants exist which operate continuously.
        Thus, there are some operating data available from communities
        and engineers already involved in the use of the process.  Though
        such systems are being commercially utilized, they may be
        technologically complex.  To operate properly, they will require
        maximum use of available information leading to careful  design
        and operation by knowledgeable professionals.  There may be only
        limited operating experience with some parts of these plants.
        Thus, technological uncertainties may still exist.

     .  Developmental Technology

        Developmental technologies have been proven in pilot operations
        or in related but different applications (for example, using
        raw materials other than mixed municipal solid waste).  There
        is sufficient experience to predict full-scale system per-
        formance, but such performance has not been confirmed.
        System design requires considerable engineering judgment
        concerning scale-up parameters and performance projections;
        consequently, the level of technical and economic uncertainty
        is generally greater than commercially operational technologies.

     •  Experimental Technology

        This category includes new technologies that are still being
        tested at the laboratory and pilot plant level.  Insufficient
        information exists to predict technical or economic viability.
        Therefore, such technologies should not be considered by cities
        contemplating immediate construction.

     The systems described in this guide are further categorized into
energy recovery and material recovery.  The two are not mutually
exclusive; most proposed resource recovery systems have aspects  of both.

                          Energy Recovery Systems

     Energy recovery technologies are classified in this report  as

     .   Waterwall  Combustion System

        Commonly called "waterwall  incinerators," this system involves
        burning of solid waste in a specially designed furnace jacketed

with water-filled tubes, and incorporating other boiler tubes to
recover heat.  In most systems built to date solid waste is
burned without prior processing, on mechanical  grates which
move it through the furnace.  A relatively recent innovation
to this process involves the burning of shredded solid waste
using semi-suspension type spreader stokers.  In both types
of systems little or no supplemental fossil  fuel is used
and heat is recovered as steam which can be  used directly or
can be converted to electricity.

Solid Refuse Derived Fuel  (RDF) System

This designates a processing system employing size reduction and
classification of waste to produce both a combustible fraction
and a "heavies" fraction which may be processed for materials
recovery.  This may be either a "wet" or a "dry" process.
These systems are also called "supplemental  fuel" systems,
since the combustible fraction would typically  be marketed
as a fuel to outside users e.g. utilities and industries, for
use as a supplement to coal  (or possibly oil) in their existing
boilers.  Some waterwall combustion systems  (as mentioned
above) would also involve such a processing  system, though
the waste might be shredded more coarsely, and  may or may
not be classified.  Similarly, some of the pyrolysis systems
may employ elements of this "front end" processing to
prepare waste for the pyrolysis reaction.  In this report
the terminology "refused derived fuel (RDF)  system" is used
to represent the preparation of a solid fuel to be marketed
to a utility or industry for use as a supplement to a fossil

Pyrolysis Systems

Pyrolysis is a broad term given to a variety of processes
where either processed or unprocessed waste  is  decomposed
by the action of heat in an oxygen deficient atmosphere.
This results in production of combustible gases or liquids
depending on operating conditions.  These products may be
either burned immediately to produce steam or,  thos.e whose
quality is high enough, may be transported or stored for
use elsewhere.

Biological Conversion Systems

Biological conversion involves the decomposition of solid
waste by bacterial action to produce combustible gases.  These
gases could be burned immediately to produce steam, or trans-
ported for use elsewhere if their quality is high enough.
Biological conversion occurs in landfills, and  gas wells may
be used to collect the gas if conditions are correct.  Alter-
natively, digestion can take place in controlled vessels.

      .  Waste-Fired Gas Turbine

        This  technology involves the burning of solid waste in a special
        incinerator and the use of the resulting hot gases to drive
        a gas turbine for energy production (Brayton Cycle).

      Typically,  people tend to classify recovery systems by processing
technique, as we have done here.  However, since market availability
is the  key pre-requisite for selecting a system, it is valuable to
look  at technologies in terms of products produced.  Viewed in this
way the following array of technologies results:

     Steam or Electricity
     generated  "on-site"
     for sale
       Technology (Process)

Waterwall combustion system (bulk
Waterwall combustion system
  (processed waste)
Pyrolysis to low Btu gas, which is
  burned in afterburner
Bio-conversion to a  gas, which is
  burned in an afterburner
     Production of a solid fuel
     for use  "off-site" as a
     supplement to coal or oil

     Production of a gas or liquid
     fuel for use "off-site" as a
     supplement to oil or gas
Solid Refuse Derived Fuel
Pyrolysis to a
Pyrolysis to a
medium Btu
to medium Btu
Table 1 combines technologies and products in a matrix and includes major
locations where implementations have occurred.  The table also shows the
status of development of the technologies.  Clearly, most of the systems
are still in relatively early stages of development, indicating the
presence of technological risk, and therefore, the need for cities to
proceed cautiously.  Status is further discussed below.

     Commercially Operational Technology.  Combustion of solid waste on
mechanical grates in waterwall furnaces to recover steam is the most
thoroughly proven resource recovery technology.  However, most of
the experience has been in Europe rather than the U.S.  Approximately
200 of these systems have been installed in Europe, and another 50
exist in Japan, Brazil and elsewhere.  Six waterwall combustion
systems are now operating in the United States, where market and'
institutional arrangements have been less attractive than other

     Although this is a proven technology, some technical uncertainties
still  exist.  Boiler corrosion and air pollution control problems,

                                              TABLE 1







... - . .-_ _ -



Used extensively in
Europe and Japan

Hempstead, N.Y. (C)
Dade Co.,Fla. (D)

St. Louis, Mo. (P.O.)
St. Louis, Mo (D)
Chicago, III (C)
Ames, Iowa (S)
Milwaukee, Wis (C)
Monroe County, N.Y

Luxembourg (C)



Los Angeles, Cal

Menlo Park, Cal (P)
o> «;
+3 2 —
o a> £•
< 3 a i-
UJ i. C tj
h- o S »
CO ^- +5 at
Braintree, Mass (O)
Harrisburg, Pa (O)
Norfolk, Va (0)
Chicago, III (0)
Nashville, Tenn (O)
Portsmouth, Va (C)
Saugus, Mass (S)
Montreal, Can. (O)
Quebec, Can (O)
Hamilton, Ont. (O)
Tokyo, Japan (O)
Akron, Ohio (D)

Columbus, Oh (D)
Akron, Oh (D)

Baltimore, Md (S)
Grasse:, France (C)




ui | 1
^ | a. ,. £
— S ™ c "5
-" - = n o
8 £! fil


Los Gatos, Cal (P.O.


Bridgeport, Conn. (D)
E. Bridgewater, Mass. (S)
Palmer Twp., Pa (D)








S. CharlestonlW Va

Angeles, Cal (O)
Phoenix, Ariz(S)
Franklin, Oh (P)
Beach, Fla (P-D)





San Diego
Cal (P,C)






      *Operating status is designated as:

          P—Pilot or Demonstration





      tN/A-Not Applicable

for instance, have resulted from improper design and/or operation of
some systems.  The overall operating experience of waterwall incinerators
varies.  Examples can be found of both very successful operations and
those that have experienced problems.  Proper design and operation,
utilizing information from the most successful operations is the key
to success.

     A recent variation of the standard waterwall combustion system
involves course shredding of waste followed by burning in a special
waterwall boiler.  Usually, this would be a "stoker boiler" where the
course shredded waste (which may have had some metals and glass removed)
is mechanically or pneumaticly thrown into a furnace and burned on a
moving grate.  There are several of these systems operating now or
scheduled for construction in the near future, but the basic boiler
technology is similar to bulk burning waterwall boilers.  Also, such
boilers have been used to burn bark and other waste and are standard
coal burning technology.

     Another system in a similar stage of development is the prepara-
tion and use of Refuse-Derived Fuel (RDF).  This concept involves
size reduction of solid waste using either hamrnermills (dry) or
hydropulpers (wet) and removal of non-combustibles to produce a
supplementary fuel for use in coal-fired steam generators (boilers).
Although the operating experience of this technology is represented
by only one full-scale demonstration plant and one commercial facility
operational since early 1976, sufficient data have been collected
and observations made to indicate that the concept can be feasible.
RDF can be produced and, according to some electric utility officials,
experience indicates that it can be fired at rates of 5 to 20 percent
of a steam generator's heat output without measurably affecting
boiler operation and short-term maintenance requirements.

     However, it should be noted that the design and operating
parameters have not yet been well defined for the most cost-effective
approach to RDF production, storage, transportation, or firing.
The technology will be optimized through the experiences of the second
and third generation plants in operation and under construction.

     In addition, it should be noted that many steam generator operators
are wary of the potential adverse effects of RDF on boiler operation and
maintenance.  This is understandable given the limited RDF firing
experience to date.  Most potential users are concerned enough that
they require RDF firing test periods of from several months to several
years during which they will evaluate the effects of RDF firing.  The
RDF purchase agreements usually allow the user to terminate the
contract if sufficient problems are found to make the RDF economically
unattractive.  It is expected that as RDF firing experience is gained,
these test period requirements will be dropped from purchase contracts.

     Although this discussion so far has centered on fluff RDF
(shredded air classified waste), a number of alternative RDF products
and production systems are discussed in this report.  There has been
relatively little experience either with the production or the firing
of these other RDF variations.   Because they entail  greater uncertainty,
they should be classified as "developmental."  The variations include
densification of the fuel into pellets, briquettes,  or cubettes for
co-firing with coal in a stoker equipped boiler; use of RDF in oil-
fired boilers, or in conventional  stoker or grate equipped boilers;
.use of RDF in cement kilns; and the production of a  very fine
powdered fuel (dust RDF) for use alone or slurried in oil.

     Developmental Technologies.  This category includes the types
of special solid refuse derived fuels described above as well as
all types of pyrolysis systems and the recovery of methane from
sanitary landfills.

     Numerous pyrolysis systems are being developed.  They are
classified as developmental because the processes are still in
the laboratory or pilot plant stages.  However, one  ,pyrolysis system
(Monsanto's Langard system) is being demonstrated at the 1,000 ton
per day scale in Baltimore, Maryland.  This plant is currently
undergoing extensive modifications to correct problems which arose
during its initial start-up period.  An assessment of the Systems'
availability cannot be made until  the modifications  are completed
and their performance is evaluated.

     A 200 ton per day demonstration of the Occidental Petroleum
Corporation's pyrolysis process is under construction in San Diego,
California and will begin operations in the fall of  1976.  Union
Carbide Corporation has already operated a 200 ton per day oxygen fed
pyrolysis plant in South Charleston, West Virginia.   In Europe, one
200 ton per day commercial Torrax pyrolysis plant (Andco Incorporated)
is nearing completion, and two other units are soon  to be started.
Several other small-scale pyrolysis systems are currently being

     Communities may wish to consider some of these  processes for
implementation, realizing that the technological uncertainties
generally exceed those for commercially operational  technologies.
Both Andco and Union Carbide consider development and demonstration
of their respective systems to be far enough along to warrant
marketing of full size plants.

     Recovery of methane from sanitary landfills is  also considered
developmental because although the technology is not complicated,
it is not yet possible to evaluate the feasibility of such a system.
Long-term monitoring is necessary to determine projected yields
over extended periods of time.   Also, more information is needed
to define the parameters (such as depth of fill, soil characteristics,
field moisture, etc.) necessary to predict yields and thus system
economics.  Nonetheless, at least one compnay (the NRG Nufuel Company)


has sufficient confidence in the process that they are seeking
landfill sites suitable for commercial application.

     Experimental Technologies.  Anaerobic digestion in controlled
reactors, and direct generation of electricity in a high pressure
gas turbine are presently being pursued at the research level.
Neither of these systems will be ready for commercial  consideration
until they are first proven in operating pilot plants.

                        Materials Recovery Systems

     Mechanical processing of mixed or partially concentrated waste
is often combined with energy recovery in comprehensive recovery
plants.  However, total materials recovery systems are also possible.
Table 2 is a list of material recovery processes with some brief
notes concerning installations and products.

Commercially Operational Technology

     Composting of waste has been practiced commercially in both the
United  States and Europe, and thus, can be considered commercially
operational technology.  Unfortunately, composting does not have
wide applicability because of the limited market for the humus
product.   In the 1960's, many composting systems were built and
operated in the United States.  All but the Altoona, Pennsylvania,
plant have been closed because of lack of market for the compost.

     Of the unit processes for recovering materials, ferrous metals
recovery is clearly a proven technology.  Ferrous metal recovery has
been demonstrated to be commercially  available and economically viable.
Systems are in use to recover ferrous metal from incinerator residue,
from coarsely ground solid waste prior to disposal in a shredded waste
landfill,  following shredding operations in refuse derived fuel
systems and even from raw unprocessed solid waste in areas where
a  high  market value and high ferrous  metal content make the operation
feasible.  The major concern in considering ferrous metal recovery is
to carefully define the market specifications for the project prior
to implementation of the subsystem, so that the equipment can be
designed to extract a marketable product.

     Wet processing for fiber recovery is a patented process of the
Black-Clawson Company.  This process  has been demonstrated in only
on instance to date.  A 150  ton per day plant has operated success-
fully on a daily basis in Franklin, Ohio, for approximately five
years.  The plant produces a  low grade paper fiber which is used
by a roofing felt manufacturer located near the Franklin plant.
However, markets for this low-grade fiber are limited.  Despite the
relatively small scale and singularity of the Franklin demonstration,
the technical success of the project  suggests that  it  is near to

                              TABLE 2.
\ iy(je
System or Subsystem ^v
Type \.
l~~ Fiber Recovery
J < Wet Separation
*f. "Z-
Q O Dry Separation
rr F
^ o= Composting
^ LU
L Magnetic Separation

!~ Aluminum Recovery
< Wet Processing
[Jj Dry processing

L_ Glass Recovery

-a *. « £ .2
° § O 1 oj § a
"y -D.E^=5 o is
ir CDP*~OLl U3
5 X^^U.^ := D-
O — — fl5 O CO
tj S < u- C/D a.

Franklin, Oh (O) *
Rome, Italy (0)

Altoona, Pa (O)
others were not
financially viable
St. Louis, Mo (P,O)
Columbus, Oh (O)
Charleston, SC (O)
Atlanta, Ga (O)
San Diego County, Cal (C)
Plus Many Others

rranklin, Oh (P)
Ames, Iowa (S)
Milwaukee, Wis (C)
Monroe Co, NY (D)
New Orleans, La (D)
San Diego County, Cal (C)

New Orleans, La (D)
San Diego County, Cal (C)
Franklin, Oh (P)
""operating status is designated as:


to being commercially operational.  A large-scale plant utilizing
the wet pulping technology is scheduled for construction by Black
Clawson in Hempstead, New York.  The pulp, however, will be used as
a fuel rather than as a paper fiber.

     Developmental Technology.  Processes to recover aluminum and
glass must still be considered developmental.  A considerable amount
of pilot work is presently underway, and economically viable systems
may soon be available.  This will occur through a combination of
optimization of recovery equipment to produce purer materials and
a lessening of industry product specifications as more experience is
obtained in using these materials recovered from municipal solid

     Processes to recover glass and aluminum usually operate on a
pre-concentrated materials stream rich in metals and glass.  The
final concentration step in glass recovery technology has focussed
on two basic approaches:  froth floatation, which produces a very
pure, small particle, non-color-sorted product; and optical
sorting, which produces a large particle, color-sorted product.
The availability of froth floatation must await its full-scale
demonstration (the first such plant will begin operations in San
Diego County in late 1976) in order to test the economic and technical
viability of the process and in order to produce a sufficient
quantity of glass to test its marketability.

     Optical sorting has been demonstrated at Franklin, Ohio by
EPA and the Glass Container Manufacturing Institute.  To date,
however, the equipment has not been able to economically produce a
product which can consistently meet the specifications of the glass
industry for ceramic contaminants.  Newer, more efficient equipment
will soon be tested.  In addition, some manufacturers have begun
to show a willingness to accept glass which does not fully meet the
industry specification.

     The most promising final concentration method for recovering
aluminum from solid waste appears to be electromagnetic devices,
referred to as "aluminum magnets."  Three companies are currently
developing these devices.  The first full-size system to use such
a device is in Ames, Iowa.  As of this writing, the equipment was
still going through normal start-up procedures.

     Assessing and selecting resource recovery technologies is a
complicated endeavor which the City should undertake with the
assistance of adequate in-house or consulting expertise.  A pro-
curement of a recovery system involves many non-technological issues
such as procurement method, management, financing and risk sharing.


These issues are discussed in other sections of this series entitled
Resource Recovery Plant Implementation:   A Guide for Municipal Officials.
(SW-157.1 to SW-157.8)

     However, understanding the basic capabilities and status of
development of technologies is an important link in the implementation
chain.  This report presents a background of such information for the
municipal official.  Clearly, the local  markets and other circumstances
surrounding each situation will influence the attractiveness and
suitability of various technologies.   In short, it is difficult to
evaluate technologies in a vacuum.   However, this report is intended
to provide factual  basic information  on  various technologies as an
aid to municipal decision-making.

     The categorizing of technologies into various stages of development
in this report is an attempt to give  cities a rough idea of how much
experience there is with various technologies.   However, it is only
a general guide.

     As a whole, resource recovery technologies are still in a relatively
early stage of development and entail risks.  Such risks include the
possibility that equipment will not perform as  designed, that products
will not meet market specifications,  and that consequently a city will
suffer an economic penalty.  This penalty could range from a major
capital loss for a plant that will  not function properly and must
be "written off," to an increase of a few dollars in net costs for
additional operating expenses.

     On the other hand, there is sufficient experience with some
technologies and promising early results from some developmental
technologies that the risks involved  may not be unreasonable.  This
is particularly true of plants designed  and backed by knowledgeable,
experienced companies.

     Costs of resource recovery are discussed only briefly in this
report (Section II).  It is EPA's firm belief that attempts to
predict (and compare) costs of various types of plants in a general
way, apart for local circumstances, is more likely to mislead than
inform.  The range of assumptions regarding specific design, reliability,
markets and other factors is too great to make  such an analysis
meaningful.  We will note only that all  but the "experimental"
technologies discussed in this report have been shown or predicted
by reliable engineers to be a roughly "competitive" disposal alternative,
particularly for cities with higher disposal costs, under "reasonable"
assumptions of capital and operating  costs and  product revenues.

                                SECTION II


     To help a community evaluate and select the technology that best
meets its needs, subsequent chapters of this Guide provide descriptions
of available and developing resource recovery technologies.  However,
evaluating and selecting a technology are only part of the implementation

     There are several additional aspects of a technical  nature that
must be considered:

     1.  Markets for recovered products
     2.  Waste generation (quantity)
     3.  Waste composition
     4.  System reliability
     5.  Plant location
     6.  Land required for the plant site
     7.  Community acceptance
     8.  Plant costs and revenues

     These factors, which apply to all technologies, must be considered
in the design of any system and are discussed briefly below.

                      Markets for Recovered Products
     The successful implementation of a resource recovery system depends
upon the ability to sell the recovered products.  Revenues from the
sale of recovered products can help to offset the cost of owning and
operating the plant; without such revenues, the cost of most resource
recovery systems would be prohibitively high.

     To be marketable, products reclaimed from energy and materials
recovery systems must have qualities that are acceptable to the user.
Steam and electricity produced from solid waste are similar to those
products from other sources.  However, refuse-derived-fuels (solid,
liquid, and gaseous) have characteristics that are different from
conventional fossil fuels.  Some of the more important fuel characteris-
tics are:  ash content, higher heating value, corrosiveness, viscosity,
and moisture content.  Similarly, the quality of recovered materials
must be commensurate with user specifications.

     For all products derived from refuse, considerations such as
reliability of supply and quantity are also important.  A higher
price can usually be obtained for a certain supply than for an
unreliable source.  This is particularly true for fuel processing.
Additional information on markets is available in the Markets guide
of this series (SW-157-3).


                        Waste Generation (Quantity)

     The amount of waste that the community generates  must  be  estimated
carefully so that the resource recovery plant (and accompanying  elements
in the total solid waste management system, i.e.  transfer stations  and
sanitary landfills) can be designed at the proper size.   An oversized
plant will  nave under-utilized equipment and will  cost more than necessary.
An undersized plant will not be able to accept the quantity of waste
that must be processed.

     There are several  ways to estimate waste generation  quantities.
Some of these may appear costly;  but,  considering the  potential  costs
of over - or under-designing a plant,  estimating  waste quantifies is
an essential and prudent investment.

     Alternative methods for obtaining these data are  discussed  below.

     In many communities (and in particular smaller  ones) no weight
records are maintained.  A common procedure for determining generation
rates is to count the trucks and then, assuming they are  fully loaded,
estimate the tonnage based on the total volume of the  trucks entering
the site.  Such a procedure can be very misleading and should  be avoided.

     Communities lacking scales at their disposal  sites have several
alternatives that can be utilized instead of volume  measurements.  The
best approach, short of installing a platform scale, is to  reroute
the collection vehicles to an existing scale on a temporary basis.
A highway weigh station or a privately-operated scale, such as at a
grain elevator or trucking firm,  may be available.   The weighing
schedule should be set up to allow for enough data to  span  seasonal
and daily variations in generation rates.  If only part of  a community's
waste will  go to the recovery facility, demographic  differences  should
also be accounted for in the weighing  schedule.

     In lieu of such a weighing program individual axle weights  can
be measured using portable scales at the disposal  sites.  However,
care must be taken to make an adequate number of  weighings, even
though axle weighing is more cumbersome and time  consuming  than  the
use of platform scales.

     A final option, one which should  be used only as  a last resort,
is to utilize national  average per capita generation data applied
to the population to be served by the  facility.  This  approach
leaves considerable chance for error because local waste  generation
often is significantly different from national averages.   In addition,
quoted per capita generation rates may include different  waste sources
than those which will go to the recovery facility.   (Commercial  waste
and construction debris are two examples where confusion  could arise.)
Thus, national average data should be avoided as  a primary  estimate.


                             Waste  Composition

     Evaluation, selection, and design  of  any resource  recovery system
requires accurate data about waste  composition,  i.e., what materials
are present in the waste and in what  proportions  they occur.   This is
particularly true where materials recovery subsystems are involved,
as the composition of many valuable components  (such as ferrous metal
or aluminum) can vary significantly among  different communities.
Waste composition variations such as  heat  content,  moisture content
and ash content can impact on selection and design  of energy recovery

     Table 3 presents national average'data on waste generation and
composition.  The limitations described above on  using  these data as
a substitute for estimating local waste quantity  also apply to their
use for determining composition.
                                TABLE 3

Rubber and leather
Total nonfood product waste
Pounds Per
Capita Per Day
 Food waste
     Total product waste
 Yard waste
 Misc. inorganics


     However, the solid waste industry,  is not in agreement as to how
much, if any, waste sampling for composition should be done.   The
major drawback is cost.  A waste composition study could cost a
community $5,000 to $20,000.  This is a  small  price compared with the
millions of dollars of capital  investment that it affects.   However,
some persons argue that the combustible  fraction of the waste stream
does not change significantly in percentage from place to place and,
thus, that a facility designed to recover primarily energy (and perhaps
ferrous metals) can be designed without  such a composition analysis.
(This would be particularly true where waterwall incineration is involved.)
Although there is merit to this argument, moisture, heating value, and
ash content are important data for design of energy recovery systems and
should be determined.

     If recovery of aluminum or glass is being considered,  a composition
analysis is far more critical,  as these  materials vary significantly
in precentage composition from place to  place, and quantity in the
waste stream would bear heavily on economic feasibility of recovery.

     Clearly, the safest route is to conduct a waste composition analysis,
and EPA believes that the benefits justify the investment.   However,
each community will make its own decision based on the cost trade-off
it sees, and the type of recovery technology it expects to employ.

                            System Reliability

     A solid waste management system must accept all  the waste that is
generated, and it must accept it when it is generated.   Reliability
of the entire solid waste management system is a function of plant
reliability plus the availability of alternative processing or disposal
facilities.  Therefore, the system,  including  the resource recovery plant
and the sanitary landfill, must be designed to operate reliably.
This discussion focuses on the reliability of  the resource recovery

     Reliability as defined here is  the  ability of the plant to accept
and process the community's waste on a regular basis.   Reliability is
achieved by a combination of the following:

     1.  Operational reliability of  the  equipment;
     2.  Redundancy of equipment or  systems; and
     3.  Storage capacity, combined  with excess processing capacity
         to handle backlogs and current  demands at the same time.

     Excess processing capacity can  be achieved by using:

     1.  Intentionally oversized equipment; and
     2.  Overtime use of primary processing lines.

     The community must specify the  degree of  reliability it requires
of the resource recovery plant and must  communicate this to the system


designer.  Because reliability is achieved only with an increase in
cost, the degree of reliability desired will have to be evaluated in
terms of capital and operating costs of the system.  Differences in
the type or degree of reliability designed into a plant is one reason
for significantly different capital costs of plants which are func-
tionally similar.

     There are no simple guidelines on the degree or type of reliability
which is best.  However, the decision maker should take care to ensure
that a reasonable degree of reliability is included in the design
even though it may increase initial costs.  A "bare bones" facility
could cause operational headaches.

                              Plant Location

     Solid waste processing plants should be located as near as
possible to centers of solid waste generation in order to minimize
haul costs and be readily accessible by major roads where the truck
traffic will present minimal environmental impacts.  The location
should also be compatible with market requirements.  For example,
waterwall boilers should be located as close as practical to steam
users to avoid large steam transmission losses and costs.  When
solid fuels or recovered metals, paper, and glass are being sold
to distant markets, access to rail sidings and major thoroughfares
should be available.  The site should be industrially zoned.
Public utilities such as power, gas, water, and sewage should be
available at reasonable installation costs.  Truck traffic through
residential areas should be minimized.

                     Land Required for the Plant Site

     The land area required for the plant site will vary with the
type of system, the size of the system, and certain site-specific
constraints such as highway access, height limitations, and typography.
The following data are rough estimates indicating the order of
magnitude of land requirements.

     Smaller processing plants (with capacities in the 200 to 500
tpd range) will generally require three to five acres of land.
Larger plants (processing over 1,000 tpd) require at least 5 to
10 acres.  Trying to squeeze a plant into too small a site can be
very costly, resulting in severe limitations on operating and main-
taining the plant.  Therefore, care should be given to providing
adequate space.

                           Community Acceptance

     Resource recovery system planners should be aware of the need
to make resource recovery plants good neighbors.  A long history of
poorly operated solid waste disposal facilities has convinced the


public that such facilities should be built "somewhere else."  Objections
which are most often voiced include increases in truck traffic, spillage
from trucks, noise, harborage of rats and vectors,  dust and air
pollution, unsightly plants, etc.

     Such factors need not be problems in properly designed recovery
plants.  Plant designers should recognize these objections and incorporate
measures to eliminate them.  Adequate allowances for attractive
architectural treatment of the buildings and landscaping (both for
decorative purposes and to screen  out noise, etc.)  are necessary.
Additional acreage, in order, to provide a buffer zone, should also be
considered.  Siting should take into account the routes the trucks must
follow.  Only commercial thoroughfares should be used and adequate
roadways should be built on the property so that trucks need not
queue up on city streets.  Adequate housekeeping of the facility and
grounds must be included in both the design .and the operating procedures.
Sound dampening enclosures should  be used to house noisy pieces of

     The decision maker must anticipate siting problems early and
design a program to deal with them properly.  Eliminating the reasons
for objections is not enough, however.  The decision maker must also
initiate aggressive communications with the public to prove to them
that their concerns will be met and their interests will be protected.
The caliber, timing, and extent of this effort may be the most critical
task in successfully implementing  a new solid waste disposal facility.
The value of professional assistance in conducting this effort should
not be overlooked.

                          Plant Cost and Revenues

     Cost is usually the major factor in decisions about whether to
implement large-scale mixed-waste  resource recovery plants.  Cost
considerations are also important  in formulating State and Federal
policies relating to such implementation.  Thus it is important that
sound methods of evaluating and comparing cost figures be used.

     Unfortunately, very little useful economic data are available as
no full-scale mixed-waste separation plants have begun regular
operation at this time.  In the absence of operating data, cost
projections must be based upon preliminary estimates by consulting
engineers and system development companies; these estimates are derived
from experience with pilot-scale operations and from equipment supplier

     A major problem in projecting costs has been the general lack
of comparability among cost estimates.  There are two apparent causes
for this.  First, 'different cost-accounting methods are employed by
various designers, making it difficult to compare cost projections in
proposals from companies bidding on the same contract.  Secondly,


most estimates  have been site-specific and reflect a wide range of
factors which vary from site to site.  Capital costs on a 1,000 ton
per day plant may range from $15 to $35 million or more, depending on
the type of system chosen,  land and site preparation costs, and
construction costs, including  labor, materials, and equipment.  Cost
ranges of this  magnitude have  been experienced even for a given type
of technology.

     Annual costs, which include amortized capital cost and operating
and maintenance costs, may  vary from $10 per input ton to $25 per
input ton, depending on, among other things, the utilization of capacity,
the interest rate on borrowed  funds, wage rates, utility rates, fuel
prices, local taxes, residual waste disposal costs, and assumptions
concerning plant reliability and maintenance costs.

     Selling prices for the recovered products are also a great source
of uncertainty.  They exhibit  large variations among geographic regions
and have been subject to extreme fluctuations over time.  Future
negotiable prices for recovered fuels and materials are subject to
additional uncertainties due to technical questions about product

     Considering all of these  variables, it is obviously difficult
to provide "typical" costs  of  various resource recovery plants.  We
believe that any such costs would be more likely to mislead than
inform.  We will note only  that the projected net costs of the 10 or
so plants under design or construction in this country are in the
$5 to $15 per ton range.

     Now that several plants are about to begin regular full-size
operation, reliable data will be becoming available.  Analysis and
dissemination of these data are high priorities of EPA's Office
of Solid Waste  Management Programs.

     Until such data is produced, planners and managers should consult,
among others, the persons and  literature mentioned in the Resource
Recovery Plant  Implementation:  Guides for Municipal Officials:
Further Assistance (SW-157.8).One publication, highly recommended
because it illustrates how net plant costs are sensitive to site
specific factors, is entitled Resource Recovery Plant Cost Estimates:
A Comparative Evaluation of Four Recent Dry-Shredding Estimates
(SW-163) by Frank A. Smith, published by EPA's Office of Solid Waste
Management Programs.

     One final  note of caution about interpreting plant cost informa-
tion.   The careful manager will not accept a capital cost figure or
a net cost per  ton figure without asking many questions about the
configuration of the system.  Typical questions include plant size,
type of technology, plant reliability, redundancy, land cost, method
of transportation of products, etc.  (As an aid to comparing cost


estimates of different systems,  the reader is encouraged to use
the Accounting Format (SW-157.6);  which is part of this Implementation
Guide series.)Furthermore,  the careful  manager will  ask whether the
reported costs are based on a preliminary process flow diagram, a final
engineering design, or some other  stage in the development of a system.
Obviously, actual  costs are the  most reliable; estimates based on a
preliminary process flow diagram are far  less reliable as predictors
of what actual costs will  eventually be;  and  so on.

                                SECTION III

                          ENERGY RECOVERY SYSTEMS
     Interest in recovering energy from municipal solid waste has
increased sharply in recent years because of the receding avail-
ability and rising cost of conventional fuels, and the continuing
problem of solid waste disposal.  Roughly 70 to 80 percent of urban
waste is combustible; reported heating values of raw urban wastes
range from 3500 Btu/lb to 6500 Btu/lb and average about 4600 Btu/lb.
Since the current rate of generation of municipal solid waste is
approximately 3.5 pounds per person per day, each person in the
community discards the energy equivalent to 1.5 pounds of coal  each
day.  As a result, solid waste is now being regarded as an energy

     The objective of energy recovery systems is to utilize the
heat of combustion (the energy) contained in the waste while
providing a means of reducing the volume of solid waste to be disposed.

     This section discusses the following alternative means of
recovering energy from municipal solid waste:  the direct generation
of steam in waterwall furnaces; preparation of solid refuse derived
fuels; pyrolysis to produce steam or gaseous, and liquid fuels;
biological gasification systems; and generation of electricity in a
turbine with gases from burning waste.  For each of the alternatives
there is a brief process description, a review of the current status of
the process, a calculation of the amount of energy recovered, and
a discussion of any special considerations or product characteristics.

                              Energy Balances

     Energy balances were calculated from data available in the
literature and from vendor contacts.  The definition of thermodynamic
efficiency is compatible with the one used in the utility industry:
the ratio of energy produced (exported) to raw energy input.  Similar
to utility practice, electrical energy and auxiliary fuel consumption
has been subtracted from the total energy produced to arrive at the
net marketable energy produced.  Also, these input energy sources
have been close-looped within the process, that is, it has been assumed
that all external energies were produced within the system.  Thus,
for example, for each process the amount of fuel produced which would
be needed to produce the electricity used in running the process is
subtracted.  The amount of fuel needed to produce a unit of electrical
energy varies for each system because each of the fuel products
has a different conversion efficiency.  By doing so, the reported
thermodynamic efficiency reflects true energy yield from a unit of
solid waste.

     Three efficiency values are reported.   Fuel  efficiency (  F)
indicates the percentage of energy in the solid waste contained in the
fuel product after accounting for in-plant energy consumption.
This fuel is then assumed to be used in a boiler to produce steam.
The efficiency of the boiler ( B) is multiplied by fuel  efficiency
to yield total system efficiency ( S) for a process converting
solid waste into steam.   Thus:

         F is the parameter which determines the amount of fuel
        produced by various processes.

         B specifies the fraction of the fuel  which can be converted
        into useful work (here assumed  to be steam).   The fuel pur-
        chaser uses this measure to evaluate the relative value of
        equivalent amounts of alternative fuels.

         S indicates the fraction of the input waste which is  converted
        into a usable end product (steam).   This  parameter enables
        different types  of energy products  to  be compared on an
        equivalent basis.

     For the sake of simplicity, the incoming  municipal  solid  waste
has been assumed to have a composition  as shown in Table 3 and a
higher heating value of  5000 Btu per pound.   Table 4 presents  a summary
of the energy efficiencies for the various  processes.

             Waterwall Combustion Systems - Unprocessed Haste

     •Traditionally, the  generation of steam from raw refuse has been
accomplished by connecting waste heat boilers  to  refractory-lined,
stoker-fired incinerators.  However, increasingly stringent air
pollution standards created a need for  a more  effective combustion
unit—the waterwall furnace.  This type of  furnace has virtually
replaced the use of refractory-lined furnaces  because these units
(1) are easier and cheaper to maintain, (2)  are smaller and less
costly to build and (3)  are more efficient  in  recovering the energy
available in the solid waste.

     Although this technology was developed more than 50 years ago
for use with low grade coal and other types of waste fuels, it
has only been used for municipal solid  waste for about 20 years.
However, in Europe and Japan its acceptance has been rapid and
widespread and several hundred units have been built in sizes  ranging
from 60 to 2600 tons per day.  In the United States and Canada 10
plants have been built,_all since 1967.

     Steam is produced at a rate of from one to three pounds per
pound of solid waste,.depending on design and  operating conditions,
and the heat value of the solid waste.   The steam can be used  directly

                               TABLE 4
Water Wall Combustion
Fluff RDF
Dust RDF
Purox Gasifier
Monsanto Gasifier
Torrax Gasifier
Oxy Pyrolysis
Biological Gasification*
With use of residue
Without use of residue
Brayton Cycle/combined cycle
Waste Fired Gas Turbine

Net Fuel
(Expressed as pe
incoming solid wa

Total Amount
Available as Steam
"cent of heat value of

19 plus
12 directly
* Includes energy recovered from sewage sludge.

 in turbines to drive the major items of equipment in the  plant, or
 it can be used in a turbo-generator to produce electricity  for in-
 plant use.  There is sufficient steam produced, however,  that most
 of it is available for off-site use, either as steam or as  electricity.
 If this excess steam cannot be sold to a nearby industry  or utility
 or used in other municipal  facilities, then it must be condensed and
 cooled before it can be recirculated to the furnace.

     Process Description.   Municipal solid waste is deposited on a
 tipping floor or in a large storage pit from which it is  transferred
 to the furnace feed hopper  (Figure 1).  From the feed hopper, the
 waste is fed onto mechanical  grates where it burns as it  moves
 continuously through the furnace.  Noncombustible material  falls off
 the end of the grate where  it is quenched with water and  then conveyed
•to trucks or a temporary storage pit.  Ferrous metal is routinely
 recovered from the residue  and in Europe the ash is often used as
 a road building material.

                     Figure 1.  Typical Waterwall Furnace for Unprocessed Solid Waste

     Waterwall furnaces are enclosed by closely spaced water filled
tubes.  Water circulating through the tubes recovers heat radiated
from the burning waste.  Integrally constructed (attached) heat
recovery boilers generate steam while reducing the temperature (and
the volume) of the exhaust gases.  The boilers consist of various
zones or tube packages referred to as heaters, economizers, reheaters,
etc. depending on the function of the particular zone.  Marketable
product (steam) is created while permitting the use of smaller gas
cleaning equipment (gas volume is proportional to absolute temperature).

     In the combustion process, oxygen (air) is required to burn the
fuel and release heat.  Air is introduced into the furnace beneath the
grates (underfire air) to aid in combustion and help keep the grates
cool.  Air is also introduced above the fuel bed (overfire air) to
promote mixing of the gases (turbulence) and to complete combustion
in the furnace.

     The combustion gases, after being cooled as they pass through
the various boiler sections, are passed through air pollution control
devices (generally electrostatic precipitators) and are then vented
to the atmosphere through a stack.

     Status.  The use of waterwall furnaces for the recovery
of steam from the combustion of solid waste has been practiced
widely in Europe for over 20 years.  Conditions that facilitated
development of steam recovery facilities in Europe include the lack
of availabile land for landfills, the relatively high costs of fossil
fuels, and institutional factors (the responsibility for both refuse
disposal and power generation are often in the hands of one governmental
entity).  More than 50 waterwall incinerators are operating in the
Federal Republic of Germany alone.

     Application of waterwall incinerator technology in the United
States for the recovery of waste heat has been recently encouraged
by the success of European experience.  The first large-scale United
States solid waste burning furnace utilizing waterwalls and
recovering steam is at the U.S. Naval Station, Norfolk, Virginia.
This 360 ton per day plant has operated successfully since 1967.   The
steam produced is used to satisfy the station's requirements for
heating and cooling.  Other facilities have been successfully operated
for several years, but, for nontechnical reasons, steam has been sold
only intermittently.  These facilities are located in Chicago, Illinois;
Braintree, Massachusetts; and Harrisburg, Pennsylvania.

     In Nashville, Tennessee, a 720 ton per day facility has been in
operation since 1974.  Steam from this plant is distributed through
a utility loop to several dozen large government and private buildings.
During the summer the steam is used to operate a chiller so that cooled
water can be distributed for air conditioning use.  This plant has

experienced severe design and operating problems.   Failure to employ
design features already proven in other plants,  largely due to an
attempt to cut costs, is the primary reason for  the problems experienced.

     Another new steam generating incinerator, which is located in
Saugus, Massachusetts, sells superheated steam to  an adjacent industrial
user.  The market was obtained before the plant  was built.  This plant,
which began operating in 1976, was privately constructed as a profit-
making venture.  It is owned jointly by a combustion systems manufacturer
and a waste disposal  contractor.

     The overall operating experience of waterwall  combustion systems
in the U.S. and Europe varies.  There are examples  of both good and
bad operations.  That is, some units have performed reliably, been
economically acceptable, and sold steam or electricity to a user on
a regular basis.  This is particularly true of units in Europe installed
within the past 5 to 8 years by reliable, experienced companies.  Other
facilities which have been either designed or operated poorly or which
have not developed markets for their steam output  have exhibited
technical or economic problems.

     Waterwall combustion systems or components  are available from
a variety of manufacturers.   Wheelabrator-Frye  (representing the
Von Roll Company of Zurich)  and Universal Oil Products (representing
the Josef Martin Company of Munich)  are marketing  complete systems.
Components (boilers and stokers)  are available from Babcox and Wilcox,
Combustion Engineering, Foster-Wheeler, Riley Stoker and Detroit Stoker.

     Energy Balance.   Figure 2 shows an energy balance for a waterwall
furnace burning mixed municipal solid waste.  In a  well designed and
operated unit, more than 97  percent of the combustible matter is
consumed to liberate heat for steam generation.  European design and
operating practices indicate that approximately  62  percent of the energy
in the refuse can be converted into steam.  After  accounting for the
energy used to operate the waterwall furnace, 59 percent of the input '
energy is available for sale to a customer.  This  is among the highest
energy efficiencies of any of the systems discussed in this report.

     Recent design changes have been made by Wheel abrator-Frye in the
plant they have installed in Saugus, Massachusetts, which may enable
the waterwall furnace to operate at 70 percent excess air.  If these
changes resolve the severe corrosion problems encountered in previous
attempts to operate at low excess air, then up to  67 percent energy
recovery could be realized.

     Residues produced from the combustion of refuse in waterwall
incinerators represent approximately 10 percent  by  volume of the
input waste and 25 to 35 percent of their original  weight.  Residues
consist of ash, glass, ferrous and nonferrous metals, and unburned
organic materials.  Recovery techniques use the  unit operations
described in Section IV.  Unrecovered residue must  be buried in
sanitary landfills to minimize leaching problems.


  5000 Btu
  1 LB MSW
                        DISSIPATED  ENERGY
                        167 Btu
                                        INTERNAL STEAM USE
                                        167 Btu
I663 Btu
                              WATERWALL  FURNACE
                                                                  3II2 Btu
                                             2946 BtU.

                                            >7  = 59 %
                                            ASH a  UNBURNT CARBON  LOSS
                                            125 Btu
                                            .07 LB
                      Figure 2.  Waterwall Furnance  Energy Balance
*This balance was based upon data obtained from:

Stabenow, G., Performance of the New Chicago Northwest Incinerator, In Proceedings; 1972 National
  Incinerator Conference, New  York, June 4-7, 1972. New York, American Society of Mechanical
  Engineers, p. 178-194.

Barniske,   L.,   and   W.   Schenkel,   Entwicklungsstand   der   Muellverbrennungsanlagen  mit
  Waermeverwertung  in der Bundesrepublik  Deutschland, In  Proceedings; Conversion  of  Refuse to
  Energy, .Montreux,  Switzerland,  November  3-5,  1975.  New  York,  Institute of Electrical  and
  Electronics Engineers, p. 91-96.

Stephens, W. C.,  and R. I. Simon, An Economic and  Financing Model for Implementing Solid Waste
  Management/Resource Recovery Projects, In Proceedings; Conversion of Refuse to Energy,  Montreux,
  Switzerland, November 3-5, 1975. New York, Institute of Electrical and Electronics Engineers, p.

     Product Characteristics.  Steam produced in incinerator facilities
may be used in-house or for district heating and cooling,  electricity
generation, or to drive machinery in industrial  processes.  Steam
customers are usually utilities or large industrial  complexes.   Steam
temperatures range from 250 F to 1050 F, and pressures range from 150
pounds per square inch guage (psig)  to 950 psig.  As a rule, higher
temperatures result in a more marketable steam product, but they also
result in larger maintenance expenses.  In steam distribution systems,
steam temperatures are kept low to minimize heat losses.  In electric
power plants, however, high temperatures and pressures are desirable
because they increase generating efficiency.                    ,

     While steam is an almost universally usable source of energy it
would not be economic to transport it more than  1  or 2 miles.  In
addition, the marketing of steam requires a suitable distribution or
delivery system.

     If the steam customer has no alternative or standby source of
steam than he must be assured a reliable supply.  Providing this
reliability will probably require the installation of a standby
fossil fuel fired boiler for use during emergencies.  Of course,
the value of the steam is enhanced by the increase in its  reliability.

              Waterwall Combustion Systems - Processed Waste

     Waterwall furnaces are also being designed  to burn coarsely
shredded solid waste.  The concept is that by first shredding the
solid waste (and possibly removing the ferrous metal and other
noncombustibles) a more homogeneous  and thus more  controllable fuel
can be produced.  The shredded waste is fed into the furnace by
spreader stokers which propel the waste across the combustion chamber,
where it then lands on a traveling grate.  This, type of firing is often
referred to as semi-suspension firing because the  waste is ignited
while it is falling through the chamber but combustion is  completed
while it rests on the grate.

     One such plant is currently in  use in Hamilton, Ontario on
municipal solid waste, and several others are in use for burning
industrial wastes.  Similar plants have been announced for Akron,
Ohio (construction is expected to begin in 1976) and proposed
for Niagra Falls, New York.  Also, the Black Clawson Company has
been contracted by the Town of Hempstead, New York to build, own
and operate a semi-suspension waterwall incinerator that will
burn the wet-pulped fuel produced by their patented wet pulping
process.  A similar plant is expected to be built  in Dade  County,
Florida and a 150 ton per day demonstration plant  is in operation
in Tokyo.

     In addition to producing a more attractive  fuel for the
incinerator, shredding enables recoverable materials which would


otherwise be consumed or degraded in the burning process to be extracted
prior to combustion.

     The cost of shredding the waste must be balanced against the
benefits of a more uniform fuel and "front-end" materials separation.
Also, there is less experience with these semi-suspension systems
than with burning unprocessed waste on a grate.

                     Solid Refuse Derived Fuel Systems

     Mixed municipal solid waste can be processed to produce a supple-
mentary fuel for fossil-fuel fired steam generators.  The wa-ste fuel
is commonly called refuse-derived fuel (RDF).  The fuel can/supplement
coal (and possibly oil), and has a heating value of about one half
that of coal.

     In this approach a system consists of a processing plant where
the solid waste is shredded and classified, and a separate facility
(market) where the RDF is burned.  Utility or industrial steam
generators provide a potential market for the RDF.  These steam
generators must be proximate to the source of solid waste and have
adequate capacity, load factor, and ash handling systems.  An
attractive feature of this system is that the capital, operating and
maintenance costs of the steam generation and auxiliary equipment are
already being borne by the user of the RDF.  This can be particularly
significant in terms of capital costs.  However,-the cost of modifying
an existing generator or designing a new generator to fire RDF, as
well as the incremental costs of operation and maintenance attributable
to firing the RDF will be passed back to the waste processing system,
usually by reducing the price paid for the RDF.

     Users could be expected to pay the same for RDF as they pay for
the primary fossil fuel, on a fuel value basis.  Of course all costs
and savings associated with handling the RDF would be deducted to
determine the net value.

     Because the steam generator is designed to fire fossil fuel
primarily, the RDF must have the physical and combustion properties
necessary to make it compatible with the specific boiler-furnace
firing and ash handling system being considered.

     Consequently, several types of RDF are being offered to potential
users:  fluff RDF, densified RDF, and dust RDF.

Fluff RDF - Dry Processing Systems

     Fluff RDF is waste that has been processed so that it will burn
efficiently in suspension as it falls down through the fire-ball
(center of turbulent flame patterns) of a boiler-furnace.  It can
be fired into the large utility-class boilers (greater than 500


million Btu per hour input or 50 megawatts of power output)  including
both suspension fired and cyclone fired boilers, and in certain stoker
and spreader-stoker fired boilers.

     Fluff RDF can be defined for purposes of this discussion as RDF
with a particle size of from 1/4 inch to 2 inches (but generally about
1 inch) and with most of the heavy,  dense materials, both organic and
inorganic, removed.

     The particle size and the degree to which the heavy, dense materials
are removed depends upon the specific characteristics of the boiler-
furnace that will fire the RDF.   For example, very large utility
boilers may befable to efficiently  burn RDF with a relatively large
particle size and containing some of the wood, rubber, and plastics.
This is because larger furnaces  have more turbulent fire-balls and
the RDF particles are suspended  in  the furnaces and subjected to
the 2200 to 2600 degree temperatures longer.

     Because stoker fired boilers have relatively small  furnaces,
the RDF has very little time to  burn as it falls through the
furnace.  Instead, grates at the bottom of the furnace hold  the
burning particles until they are completely combusted.

     Process Description.  The RDF  dry processing concept was originally
demonstrated at St. Louis, Missouri  where solid waste was passed through
a single shredder to reduce the  particle size to 1-1/2 inches.  The
shredded material was then injected  into an air classifier where a
vertical column of turbulent air separated the light RDF from the
inorganics and the heavy, dense  organics that will  not completely
burn in suspension.  About 80 to 85  percent of the shredded  waste was
separated as RDF.

     The RDF was fired in two Union  Electric Company 125 megawatt
pulverized coal-fired boilers at rates ranging from 5 to 27  percent
on a power output basis.

     A typical RDF system may use primary shredding to reduce the
particle size to four to eight inches, followed by an air classifier
that separates from 50 to 85 percent of the shredded material as RDF
(Figure 3).  To increase its heat value and reduce its abrasiveness
during pneumatic firing,  the shredded material is then passed over a
screen or trommel to remove glass fines. -After screening, the RDF
is passed through a secondary shredder to reduce the particle size
to a range of from 1/4 inch to 2 inches, depending on the requirements
of the specific boiler being considered.  The RDF is then stored,
transported, and fired, as required.

     Status.  Based on the general  success of the St. Louis  demonstration
project, the fluff RDF approach  is  being implemented in several cities.


                        1'  Figure 3.  This simplified flow diagram shows how the dry processing
                        approach (no water slurry) can be used to produce fluff, densified, or dust RDF.

Consulting engineers are recommending implementation of the concept
where feasible.  In addition,  about ten companies  are marketing systems
that they will design and construct for a fixed price.

     One additional plant is already in operation*;in Ames,  Iowa, and
Plants in Milwaukee and Chicago,  are scheduled  for completion in 1976.
However, the experience with RDF  technology is  limited.   Though a
process of shredding and air classification can produce a sized, mostly
organic fuel, the process is far  from optimized.   Furthermore,  burning
of this fuel as a supplement to coal is still  in  its infancy.  Thus,
willing buyers are not readily available.

     Design questions that remain to be answered  and some comments
on RDF plant considerations follow:

     -  Shredding.   Is two stage  shredding (primary followed by
        secondary)  actually more  cost effective than a single stage?
        What is the most cost  effective hammer  configuration and hammer
        retipping material? What is the optimum  final  RDF  particle
        size for each boiler firing system?

     -  Air Classification. Which configuration  (design) is most
        efficient?  What is the optimum degree  of  removal of non-
        burnables for each boiler firing system?   Where should
        the air classifier be  located in the waste processing system—
        between the shredders, after secondary  shredding, before
        or after screening?

     -  Screening.   Is screening  cost effective?   What kind of  screen
        is most cost effective?  Where should  the  screen be located--
        before primary shredding, between shredders, etc.?

     -  Storage.  Fluff RDF is a  very difficult material to handle—
        it bridges easily (hangs  up in hoppers),  has a negative
        angle of repose (in a  bin, the top of  a pile of RDF will not
        fall when the RDF directly underneath  it  has been removed),
        it does not flow easily,  and it binds  like paper-mache1 after
        several days of storage and when wet.   The best way to  handle
        RDF would be to keep it in motion at all  times.   However, this
        is not practical, so when storage is required, it should
        be stored in a bin in  which the unloading  device is able to
        retrieve the RDF from  every point on the  bottom on  the  bin.
        In addition, to avoid  bridging, the sides  of the bin must
        flare outward toward the  bottom.

     -  Firing.  Erosion of the elbows (curves)'of the pneumatic
        firing system can become  a major maintenance problem unless
        replaceable elbows and an abrasion resistant material are
        used at these high wear points.  Which  abrasion resistant
        material is most cost effective?  Another consideration
        is the optimum elevation  of the RDF firing nozzles  to enhance
        RDF combustion but to minimize ash carryover in the form of
        particulate stack emissions.


-  Stack  Emissions.  Based on evaluations at St. Louis, sulphur
   oxides,  nitrogen oxides, mercury vapor, and chloride emissions
   are  not  significantly changed when RDF is fired with coal at
   rates  of from 5 to 27 percent on a power output basis.   In
   addition, particulate emissions did not significantly increase
   at all RDF firing rates as long as the boiler loading was at
   or below its design capacity of 125 mw.  However there was an
   increase in emissions when the boiler was run at 140 mw  using
   RDF  and  coal, as opposed to coal only.  Unfortunately, this
   boiler is routinely operated at this higher load.

     These  higher emissions must have resulted from a decrease
   in electrostatic precipitator collection efficiency because
   the  uncontrolled emissions (inlet to the precipitator) did
   not  increase significantly, even at the higher boiler loading.
   It is  felt that precipitator efficiency decreased because the
   volumetric gas flow rate increases when RDF is used to supplement
   the  coal.  This increase in gas flow rate is due, in part,
   to the fact that the moisture content of the RDF (on a heat
   value  basis) is six times that of coal.

     If this decrease in precipitator efficiency results in
   emissions that exceed standards, a number of steps could
   be taken  to correct the problem:  (1) RDF could be fired
   only at  lower boiler loads so that the combined firing
   exhaust  gases do not exceed the precipitator's design flow
   rate;  (2) modifications could be made to the precipitator
   to increase its collection efficiency; or (3)  the RDF could
   be dried  to reduce the quantity of exhaust gases.   Each
   situation must be investigated individually to determine
   the most cost effective approach.

-  Bottom Ash.   If an accumulation of unburned RDF organics and
   ash would overload the bottom ash handling facilities,
   the accumulation could be logically reduced by taking one
   of several steps to improve the combustion of the RDF:
   (1) reduce the quantity of heavy dense materials recovered
   with the RDF by adjusting the air flow rate of the air
   classifier during waste processing and thus recovering a
   lower percentage of waste as RDF;  (2) increase the surface
   area of the RDF particles by reducing the RDF particle size;
   or (3)  increase the retention time of the RDF in the boiler
   by raising the elevation of the RDF firing nozzels.

-  Boiler Operation.   At St. Louis the Union Electric Company
   has indicated that they have not experienced any problems
   with maintaining power levels,  slagging,  erosion within  the
   boiler, fouling, or corrosion.

      Energy  Balance.  An energy balance has  been  developed  for  a
typical  fluff RDF  system (See Figure 4).   It is based  on a  system
having  two stage shredding;  a trommel  screen;  air classification;
and truck transport to  a user 15  miles  away.   Sixty-two percent of
the raw waste is assumed recovered as  RDF.
  152 Btu
                                            392 Btj

                                 3897 Btu
   1147  Btu
                                                     3505 Btu
                                 0.62 LB
                  1144 Btu
                  0.38 LB
                                       10 Btu
                                      0.04 LB
                       Figure 4.  Fluff RDF Energy Balance
*This balance was based upon data obtained from:

Shannon, L. J., M. P. Schrag, F. I. Honea, and D. Bendersky, St. Louis/Union Electric Refuse Firinq_
 Demonstration Air Pollution Test  Report, August 1974. Washington, Office of Research and
 Development, U. S. Environmental Protection Agency. 108 p.

Proceedings; National Center for Resource Recovery, Inc., Seminar, U. S. Environmental Protection
 Agency,  Municipal  Environmental Research Laboratory, Cincinnati, Ohio, December 3-4, 1975.
 Session V, "Unit Processes for Materials Recovery."

Rigo, H. G.,  Technical Evaluation of the Feasibility of Burning Eco-Fuel at Philadelphia Naval
 Shipyard, January 1974. Construction Engineering Research Laboratory, Letter Report E-25. 54 p.
      Product  Characteristics.   RDF is clearly an  inferior  fuel  to
coal in  practically every parameter except  sulfur content  (Table 5).
However,  when fired at  low rates--!0 to  20  percent of  power output-
boiler operation  and maintenance  problems are not expected to  increase
measurably.   However, there  is only very limited  experience to  verify

                                TABLE 5.

Heating Value (Btu/lb)
Bulk Density (Lb/Ft3)
Average Size (In.)

Per Pound
Fluff RDF
5,000 - 6,500
20 - 30%
11,500- 14,300
3 - 1 2%

6.2 - 81
4.3 - 6.0
4.8- 17.4
Per Million Btu
Fluff RDF

31 - 60 Lb

11 -14
2.5 - .35

2- 10 Lb

.4 - 3.7
Fluff RDF - Wet Processing Systems

     Fluff RDF can also be produced by a  wet  processing system where
the waste is converted into a slurry.

     Process Description.   Wet processing to  produce  RDF involves
size reduction, removal of non-combustibles,  and  dewatering steps.
Solid waste is conveyed to a wet pulping  machine  (hydropulper) where it
is mixed with water (see Figure 5).  The  waste material is reduced to an
aqueous slurry by the action of high speed cutting  blades located at the
bottom of the pulper.  Large items, such  as tin cans, rocks and other
inorganics, are ejected through an opening in the side of the hydropulper.
Ferrous metals can be recovered from this material.

     The remaining slurry is pumped to a  liquid cyclone where heavier
materials such as glass, nonferrous metals, thick plastics, wood, etc.,
are removed by centrifugal action.  The heavy fraction can be processed
to recover aluminum and glass.  The lighter,  mostly paper fraction is
then dewatered to the desired moisture content and  used as RDF.

            TIPPING FLOOR
                                                       BARREL PRESS
                                                                             TO RECOVERY OF
                                                                              - ALUMINUM
                                                                               SMALL FERROUS METALS
                                                NONFERROUS MATERIALS
                                                   RETURN TO PROCESS

                                                 FERROUS METAL
                                                                                                                     LOW PRESSURE
                                                                                                                     TO PROCESS
                                                Figure 5.  Wet Process Energy Recovery System

     Although dewatering the s-lurry is expensive, the wet pulping approach
has several advantages over the dry processing approach.  Perhaps the
most important is the ability to easily handle sewage sludges.  By
blending sewage sludge with the pulped slurry, the resulting mixture
can be simultaneously dewatered for use as fuel.  Of course, the
particular sludge being considered must be investigated for materials
(like heavy metals) that may cause air pollution problems during
combustion.  However, dewatering the slurry is expensive, especially
if a 20 or 30 percent moisture content is required as may be the case
for use as supplementary fuel in some steam generators.  Consequently,
the wet processing approach to producing a supplementary fuel will
probably not be as popular as dry processing.  Rather, the RDF produced
by most wet processing systems will probably have a 50 percent moisture
content and be used as the primary fuel in steam generators designed
specifically to handle this material (see discussion on Waterwall
Combustion Systems - Processed Waste).

     Nevertheless, at least two communities Memphis, Tenessee, and
Norwalk, Connecticut have seriously studied the feasibility of wet
processing to produce RDF for use as supplementary fuel in existing
coal-fired steam generators.

     Other advantages include reduced likelihood of explosions and fires
during size reduction, fewer dust control problems, and greater flexibility
of handling and shipping.

     Status.  The basic RDF wet processing steps have been demonstrated
in a 150 ton per day EPA demonstration plant located in Franklin,  Ohio.
The plant has been consistently processing about 35 tons per day of
waste since 1971.  The Franklin plant dewaters a pulped slurry of
nonrecoverable fiber to a moisture content of about 50 percent before
burning it in a fluidized bed incinerator without heat recovery.
Nonetheless, the RDF preparation components have been successfully

     Energy Balance.  An energy balance has been developed for a
typical wet processing system (Figure 6).  Comparing this to the
energy balance for fluff RDF it can be seen that although a greater
percent of the combustible material is recovered as fuel, its lower
combustion efficiency results in a lower net yield of steam.

     Product Characteristics.  Wet process RDF is homogeneous (uniform
composition and particle size) and has an as-received heating value
of approximately 3500 Btu/lb, at a moisture content of 50 percent,
and an ash content of approximately 20 percent.  The high moisture
content of the fuel product precludes the use of this product
in many existing boilers (however, it can be used as a primary fuel
in specially designed furnaces).  Many industrial and utility boiler
operators are requesting that the material be between 15 and 20 percent
moisture.  At this moisture, the RDF can be suspension or spreader stoker
fired or it can be densified (briquetting or pelletizing) for use in


    222  Btu
  1722 Btu
                     Figure 6.  Wet Process RDF Energy Balance
 "This balance was based upon data obtained from:

 Wittmann, T. J., et al, A Technical, Environmental and Economic Evaluation of the "Wet Processing
  System for the Recovery and Disposal of Municipal Solid Waste," Final Report SW-109c, U. S.
  Environmental Protection Agency, 1975. 217 p.
chain grate,  underfed, or mechanical or pneumatic spreader  stoker
equipped  industrial and utility boilers.  Drying wet process  RDF
requires  significant amounts  of energy.  A  10  percent reduction in
moisture  content consumes between 4 and 8 percent of the fuel,  depending
on the specific design of the dryers.

Dust RDF

     A dust-like RDF has been developed by  Combustion Equipment
Associates  as a high quality  all-purpose fuel.   According to  the
developer,  it can be fired  in suspension with  coal and oil  in most
steam generators with adequate ash handling facilities.  In addition,
it may prove  feasible to slurry the fuel with  oil for firing  in
the oil-fired boilers, thus eliminating the need for separate firing
1i nes.

     Process  Description.   Solid waste is first shredded, air
classified, and screened, the same initial  steps used to produce
fluff RDF (Figure 3).  However, instead of  using a secondary  shredder
to reduce the particle size further as in fluff RDF production systems,


an embrittling agent is added to the coarse shredded material.
This chemical hardens the cellulose fibers so that the paper and cardboard
becomes friable and will shatter upon impact.  The treated material
is then run through a ball mill similar to those used by electric
utilities to pulverize coal.  The material is pulverized in the ball
mill until it will pass a 100 mesh screen.  The dust RDF product
has a particle size of less than 0.15 millimmeter.

     Status.   According to company officials, a four ton per day pilot
plant operated continuously from Spring 1974 to October 1975.

     A 20 ton per hour facility is being constructed at East
Bridgewater,  Massachusetts.  The fuel from this facility will  be
trucked 75 miles to be used as an auxiliary fuel in several oil-fired
steam generators producing industrial process steam.

     The dust RDF is to provide 60 percent of the heat input to the
generators.  Although the company is investigating the feasibility
of slurrying the dust RDF with oil, the RDF and oil will not be
premixed for this project.

     Energy Balance.  An energy balance has been developed for a
typical dust RDF system (Figure 7).  Eighty percent of the energy
is recovered in the fuel fraction.  Its excellent combustion charac-
teristics make it a very efficient fuel so that when fired in  a boiler
the steam yield would be 63 percent of the energy value of the incoming
solid waste.   This would be the highest yield of any of the systems
examined in this report.

     Product Characterists.  According to company officials, the dust
RDF has a heating value of 6,900 Btu's per pound, and contains 10
percent ash and two percent moisture.  Its bulk density is approximately
25 to 32 pounds per cubic foot.  There are no known limits on  shelf
life.  It is expected that the product can be handled and stored like
a powder using conventional pulverized coal handling equipment.

     Although dust RDF has superior combustion properties to fluff
RDF, the production costs are likely to be greater than for fluff
RDF.  Also, special care in handling and storage is necessary  to
minimize the danger of explosions.  The cost trade-off can be
determined only through operating experience with these systems.

     Densified RDF

     Processes for densifying RDF are being investigated by a
number of organizations.  By densifying RDF, it is anticipated
that some of the handling and storage problems of fluff RDF can
be avoided, that stoker and spreader-stokers can more easily fire
processed waste, and that it can be fired at higher rates than
fluff RDF.


          884 Btu
    136 Btu
  642 Btu
                                     220 E5tu_

                                     FUEL   ~!
                        0.52 LB or 4200 Btu
               800 Btu
                                               3980 Btu ^
                                                            - 797o
                                                                         3144 Btu
                                                                         T]s = 63%
                                   194 Btu
                         Figure 7.  Dust RDF Balance
 *This balance was based upon data obtained from:
                                                             p' .
 Beningson, R. M., K. J. Rogers, T. J. Lamb, and R. M. Nadkarni, Production of Eco-Fuel -II from
  Municipal Solid Waste CEA/ADL Process, in Proceedings; Conversion of Refuse to Energy, Montreux,
  Switzerland, November 3-4, 1975.  New York, Institute of Electrical and Electronics Engineers, p.
     Process Description.   Densified  RDF is  produced  by pelletizing,
briquetting, or  extruding  fluff RDF.   It is  also anticipated  that dust
RDF can  be densified by adding a chemical binder and  processing in a

     Status.  Densified RDF has been  produced  in small  quantities
at several pilot plants around the  country.  Several  trial burns in
stoker-fired steam generators have  been encouraging.   However,  this
concept  has not  yet been demonstrated on a commercial  scale.

     Several areas need to be investigated further:

     1.   Densifying Costs.   What is the cost of densifying RDF?  How
          rapidly do the dies used in  the process need replacement?
          How much energy is required?  What  kinds of  production rates
          can be  achieved with conventional equipment?

     2,  Handling and Storage.  Does the densified fuel hold together,
         or tend to break up with time or when handled?  Are the
         materials handling properties improved relative to fluff
         RDF so that lower cost storage and handling facilities can
         be used?  What is the optimum moisture content?

     3.  Firing.  Can densified RDF be premixed with crushed coal for
         firing in stoker or spreader-stoker steam generators, thus
         avoiding the cost of a separate RDF firing system?

     These questions are being addressed by a project recently initiated
by the EPA.*

     Product Characteristics.  The densified RDF will have basically
the same chemical properties of the fluff or dust RDF feedstock.  But,
the bulk density will be increased to about 35 to 42 pounds per cubic
foot, which is similar to that of coal.

                             Pyrolysis Systems

     Pyrolysis is the destructive distillation of the organic fraction
of solid waste.  It occurs when organic material is exposed to heat
in the absence or near absence of oxygen.   Pyrolysis differs from
incineration in that it is endothermic (heat absorbing) rather than
exothermic.  Processes under development use heat from part of the
waste to provide the heat absorbed during pyrolysis and recover the
remaining heat in the form of steam or a gaseous or liquid fuel.

     All processes reduce the solid waste to three forms:   gases (primarily
hydrogen, methane carbon monoxide and carbon dioxide), liquids (water,
and organic chemicals such as acetic acid and methanol), and solids
(a carbonaceous char).  The form and characteristics of the fuel fraction
varies for each of the different processes under development and is a
function of the reaction time, temperature and pressure of the
pyrolysis reactor, the particle size of the feed, and the  presence
of catalysts, and auxiliary fuels.

     To maximize gas production, reactor temperatures are  held in
the range of 1400 F to 3000 F; for oil, temperature is on  the order
of 900 F.  Pressures range from 1 to 70 atmospheres.  Ideally, the
reaction is allowed to take place in the absence of diluting gases
so that the product is the volatile matter of the solid waste.  If
air is used in the reactor, the gases produced will be diluted by the
nitrogen in the air (air is approximately 79 percent nitrogen
and 21  percent oxygen).   As a result, some processes have  been developed
     *"Preparation, Use and Cost of d-RDF as a Supplementary Fuel  in
Stoker Fired Boilers," Office of Research and Development,  U.S.  EPA.

which use oxygen, thus resulting in a higher heat content fuel  gas.
Other systems indirectly transfer the heat to the gasifier to minimize
dilution of the product gas.

     Heating solid waste releases gases and leaves a carbon residue
called char.  In some reactors,  the residue reaches such high temperatures
that the ash and other noncombustibles, such as cans and glass, melt
to form' a slag which can be removed from the reactor in a molten state
and quenched to form a glassy aggregate.

     Residues produced from pyrolysis are biologically inactive and
may be safely disposed in sanitary landfills.   Solid residues from the
noncombustible portions of the refuse, such as glassy aggregate, may
be used for construction and  paving.   If the char is not consumed in the
process, it has a higher heating value of approximately 9000 BTU/lb.
Its high ash content (50 percent), however, severely limits its
usefulness.  Clearly, failure to consume all the char in the process
represents a loss in energy recovery.

     This report describes the four pyrolysis  systems which can be
classified as "developmental."  There are presently no commercially
operational pyrolysis systems, and there are numerous other systems
which can be considered "experimental."  All four of the systems
described have been previously operated on a small pilot scale and
full size plants Of 200 tons  per day or larger have been or are being
built.  Two of the systems produce low BTU gas which is used "on-site"
to produce steam.  The third  system produces a medium BTU gas which can
be sold to a nearby industrial user or may be  suitable as a chemical
feedstock.  The fourth system produces an oil-like liquid fuel  which
can be stored and transported for use "off-site" in large industrial
or utility boilers.

Low BTU Gas - Monsanto Langard System

     Process Description.  The Monsanto Langard system employs a
controlled air primary furnace chamber (pyrolysis) and immediate
combustion of low heat value  gases in an afterburner for recovery of
heat (Figure 8).  Waste is shredded,  conveyed  to a storage silo,
and subsequently fed to a rotary kiln where it is pyrolyzed.  Fuel
oil is also burned in the kiln to provide some of the heat for the
pyrolysis reaction.  The burner is arranged to provide a counter-
current flow of gases and solids, thus exposing the waste to progressively
higher temperatures as it passes through the kiln.  The finished residue
is exposed to the highest temperature 1000 C (1800 F) just before it
is discharged from the kiln and quenched in a water-filled tank.
The residuals are split into  three fractions,  glassy aggregate, ferrous
and char.  The glassy aggregate and ferrous materials are recovered
for sale and the char is dewatered and landfilled.

                       AIR  POLLUTION CONTROL
                    WASTE HEAT  BOILER
                                                    WATER CLARIFIER
                                                                    GLASSY AGGREGATE
                                                                    AND CHAR

                                   WATER  QUENCH
 Figure 8. The Monsanto Landgard System produces a low Btu gas which is immediately
         burned on-site for the production of steam.

     Gases resulting from the pyrolysis reaction have a high temperature
(1200 F) and low heating value (120 BTU/cubic foot)  making off-site
transportation uneconomical; therefore* they are immediately mixed
with air and burned in an afterburner to liberate the heat of combustion.
The combusted gases then pass through waste heat boilers where steam is
generated for distribution.

     Product Characteristics.  Steam from the Baltimore plant is produced
at up to 200,000 Ibs.  per hour.   Saturated steam at  a temperature of
about 400 F is delivered to  the  Baltimore Gas and Electric Company's
existing downtown steam loop via a new mile long pipeline.

     While this is the most  economic arrangement for the Baltimore
facility, other end uses for the gas produced in the kiln might also
be possible.  For instance,  if a Landgard plant were built immediately
adjacent to a large utility  boiler, it. might be feasible to direct
the hot, combustible kiln off-gas directly into the  utility's boiler,
thus eliminating the need for a  separate afterburner, waste heat
boilers, and air pollution control equipment.

     Status.  A 1000 ton per day prototype plant has been built in
Baltimore, Maryland.  Construction of the plant was  completed in
February, 1975 under a turnkey contract with Monsanto.   However,
normal operation of the plant has not been possible  because a number
of process changes are needed in order to insure proper operation.
Engineers from Monsanto and  the  City of Baltimore are now working on
a series of medications in an effort to correct the  problems
plaquing the plant.

     As originally built, exhaust gases are cleaned  by means of a
large spray tower.  Initial  tests of the spray tower showed that it
could not clean the gases sufficiently to meet the required local
and Federal ordinances.  All efforts to modify plant operations to meet
the standard have failed, and as a result it has been decided that
additional air pollution control equipment must be added.

     Energy Balance.  The energy balance for the Languard system is
shown in Figure 9.  Here again it is assumed that the energy to produce
the purchased electricity and contained in the purchased quench oil
(7.2 gallons of No. 2 fuel oil per ton of solid waste)   was provided
by the system's energy product.   Losses in the process include the energy
remaining in the carbonaceous char and conversion losses experienced
in the waste heat boiler. As a  result of these losses and provisions
for the system's input energy needs, 78 percent of the energy in the
incoming waste is available  in the combustible gas.   This gas is
then burned in an afterburner and the heat is recovered as steam in
a "waste-heat" boiler.  The  burner-boiler combination has a heat
recovery efficiency of 54 percent so the net recovery of energy in
the form of steam is 42 percent  of the energy available in the "as
received" solid waste.


             130 Btu        352 Btu
     I ISC B»u

5000 Btu




554 Btu
Z ' '
° if '

4620 Btu


I ^
3905 Btu

T]f 78 7o


2095 Btu

\ 	 1 17,, =42 %

rjB -- 54%
                                            7I5 Btu
                  Figure 9.  Monsanto Landgard Energy Balance  *
 *This balance was based upon data obtained from:

 Sussman, D. B., Baltimore Demonstrates Gas Pyrolysis, Resource Recovery from Solid Waste, First
  Interim Report SW-75d.i, U. S. Environmental Protection Agency, 1975. p. 12-13.

 .Levy, S. J., San Diego County Demonstrates Pyrolysis of Solid Wastes to Recover Liquid Fuel, Metals,
  and Glass. Environmental Protection Publication SW-80d.2. Washington, U. S. Government Printing
  Office, 1975. 7 p.
Low BTU Gas  -  Andco Torrax System

      Process Description.   The principal components of the  Torrax
System are the gasifier,  secondary  combustion chamber, primary pre-
heating regenerative towers, energy recovery/conversion system, and
the gas cleaning system  (Figure 10).   The solid  waste is charged as
received from  the solid waste pit,  without prior preparation,  into
the gasifier.   The gasifier is a vertical shaft  furnace designed
so  that the descending refuse burden  and the ascending high  temperature
gases  become a counter-current heat exchanger.   The uppermost  portion
of  the descending solid waste serves  as  a plug to minimize  the infil-
tration of ambient air.  As the solid waste descends, three  distinct
process changes occur.  The first is  the drying  where the moisture is
driven off; the second is  the pyrolyzing due to  the heat transfer from
the ascending,  hot gases to the solid waste; and the third  is  combustion
in  the hearth  where the carbonaceous  char is oxidized to carbon dioxide,
and  melting of the inert fraction of  the solid waste.

                                                         STEAM TO
                                                         INDUSTRIAL PROCESSES
                                                           SECONDARY COMBUSTION CHAMBER
                           Figure 10. Jorrax Slagging Pyrolysis System

     The heat for pyrolyzing and drying the solid waste and for melting
the inert fraction is produced by the combustion of the carbon char with
2000 F preheated air supplied to the hearth zone of the gasifier.  The
heat thus generated melts the inerts to form a molten slag, which
is drained continuously through a sealed tap into a water quench tank to
produce a black, sterile, granulated residue.

     As with the Monsanto system, the BTU value of the gas is too low
to make off-site transportation of the gas economic-.  Instead the gases
are injected into an after-burner or secondary combustion chamber where
they are burned to completion.  The heat which is thus released is then
directed to a waste heat boiler where it is recovered as steam.

     A portion of the hot waste gas from the secondary combustion chamber
(about 15 percent) is directed through regenerative towers where its
sensible heat is recovered and used for preheating the process air
supplied to the gasifier hearth.  These regenerative towers, successfully
used for many years in the steel industry, but as yet untested for this
system, are two refractory lined vessels containing a high heat capacity
refractory checkerwork material ,x  Hot products of combustion from the
secondary combustion chamber and ambient process air are passed through
the towers on a cyclical basis for preheating  the 1000 C combustion air.
The remainder of the secondary combustion chamber existing flow is
supplied to a waste heat boiler designed for inlet gas temperatures
of 2100 F to 3000 F.

     The cooled waste gases from the regenerative towers are combined
with the exiting flow from the waste heat boiler and are ducted to
a hot gas electrostatic precipitator of conventional design.

     Status.  The principles of the Torrax process were originally
proven on a 75 ton per day pilot plant operated intermittently since
1971.  This plant, located in Erie County, New York has been used
to process municipal solid waste and solid waste/sewage sludge.  Test
runs with controlled percentages of waste oil, tires, and PVC plastics
were also run.  The pilot plant differs significantly from the above
described system in that the hot blast combustion air is heated using
natural-gas-fired air-to-air heat exchanger instead of the regenerative

     The Carborundum Corporation, which was involved in the original
development of the Torrax process, has recently turned its marketing
rights in the U.S. over to Andco.

     A 200 ton per day prototype plant is undergoing startup in Luxemburg
and at least two other plants are also scheduled to be built in Europe
in the near future.

      Energy Balance.   An  energy balance  for  the system  is shown  in
Figure 11.   About 15  percent  of the energy value  in the solid waste
is  utilized to  preheat the combustion air or replace the energy  needed
to  supply the purchased electricity used in  the plant.   The  heat
ultimately delivered  to the waste  heat boiler is  converted to steam
at  an efficiency of 69 percent leaving a net system output  (as steam)
of  58 percent of the  original  energy in  the  solid waste.
i 435 Btu
1302 Btu
124 Btu PURCHASED 413 Btu
5000 Btu
1 70


3 L
5030 Btu
53 Btu
I37 300
Bfu Btu |
71 Btu
j 4199 Btu ^ 	 2897 Btu ^
•tJF= 84% ~~ \ 	 | ^s 58%
418 Btu
-rjB =69%

                      Figure 1 1.  Energy Balance For The Torrax System
    *This balance was based upon data obtained from:

    Stoia,  J. Z., Torrax — A Slagging Pyrolysis System for  Converting Solid Waste to Fuel Gus,
     Carborundum Environmental  Systems, Inc., Solid Waste Conversion Division. Niagara Falls, New
     York, p. 11-22.

     Eerie  County  — Torrax Solid Waste Demonstration  Project, Final Report,  May  1974. U.  S.
     Environmental Protection Agency, Office of Solid Waste Management. 46 p.

    Legille, E. etal,  A Slagging Pyrolysis Solid Waste Conversion System, On Proceedings: Conversion of Refuse
     to Energy, Montreux, Switzerland, November 3-5, 1975, New York, Institute of Electrical and Electronics
     Engineers, p. 232-237.

Medium BTU Gas - Union Carbide Purox System

     Process Description.  The key element of the Purox System is a
vertical shaft furnace (Figure 12), wherein shredded solid waste is
fed into the top of the reactor through a piston air lock system while
oxygen is injected into the bottom of the furnace.  The solid waste
descends by gravity through the varying temperature zones on its down-
ward passage through the vertical reactor.  The oxygen reacting with
char material previously formed from refuse in an upper zone of the
reactor creates a temperature zone in the range of 3000 F in the lower
portion of the reactor.  Rising gases cool to approximately 200 F as they
move upward thereby providing the energy for pyrolyzing the incoming
waste in the upper portion of the reactor.  Metals, glass and other
materials are transformed into a molten slag by the high temperatures
generated in the lower protion of the reactor.  The molten slag mixture
continuously drains into a water quench tank where a hard granular
aggregate material referred to as "frit" is formed.

     Product Characteristics.  Gases leaving the reactor contain 30 to
40 percent moisture.  This is removed in a gas clean up step, along with
ash, tars, and other condensable liquids.  The remaining gas contains
approximately 75 percent CO and \\^ in approximately a two to one ratio;
the other 25 percent being comprised of CO?, CH^, No, and organic
compounds.  Its heating value is approximately 300 BTU/cu ft.

     Status.  In 1970, the basic system was assembled in a 5 ton per
day pilot plant at Union Carbide's Technology Development Center in
Tarrytown, New York.  Following evaluation of the pilot plant facility, a
200 ton per day Purox System was completed during 1974 in South Charleston,
West Virginia.  The West Virginia facility was designed to prove out the
corporation's full-scale modular unit, and it was intended that larger
plants would obtain greater throughput capacity by incorporating modular
additions.  Most recently, however, the Union Carbide Corporation has
decided to market a 350 ton per day module so that the unit being tested
is not the one that will be marketed.

     Union Carbide is currently concluding the second portion of a three
phase testing and performance evaluation program.  The first phase concerned
the receiving, feeding, and pyrolytic conversion of mixed municipal solid
waste without size reduction or sorting.  The second phase involved
minimal pre-processing of incoming solid waste, consisting of coarse
shredding and magnetic removal of the ferrous fraction prior to intro-
duction into the pyrolysis reactor.  The third phase anticipated to
commence in 1976, constitutes a co-disposal investigation wherein
sewage treatment plant sludges, containing varying moisture contents,
will be mixed in varying proportions with shredded solid waste.

     Energy Balance.  Energy is consumed in the Purox process primarily
in the shredding of the waste and in producing the 0.2 Ibs.  of oxygen
that is required for each pound of solid waste burned (Figure 13).   Each
pound of solid waste processed yields about 11.4 cubic feet of gas having
a heating value of about 300 Btu/cu.ft.   Because this fuel  burns so well,
if used directly in a boiler the combustion efficiency would be on the
order of 90 percent, with a net system efficiency of about 58 percent.


                                                                                              PRODUCT GAS
                                                                                               TO USER
                              PYRO LYSIS
                                                                                      *• WASTEWATER
              Figure 12.  Union Carbide Purox System produces a medium Btu gas for sale to off site users.


5000 Btu

0.2 LB


Sii BTu



499 Btu
* n

C"M p\

I i

3722 Btu 3223 Btu
1 1. 4 CUBIC FEET Tj 64% """

o i E.MIVI
BOILER 290' Bf" _
1 — V ^s 58 %

1?B = 90%

0.30 LB 0.20 LB
~50Btu I5I Btu
                    Figure 13.  Energy Balance for the Purox Gasifier
*This balance was based upon data obtained from:

Snyder, N. W.,  J. J. Brehany, and R. E.  Mitchell, East Bay Solid Waste Energy Conversion System, In
 Proceedings; Conversion  of Refuse  to  Energy, Montreux, Switzerland, November 3-5, 1975. New
 York, Institute of Electrical and Electronics Engineers, p. 428-433.

Bonnet, F. W.,  Partial Oxvdation of Refuse Using the Purox System, given at Conversion of Refuse to
 Energy Conference,Montreux, Switzerland, November 3-5, 1975, but not in  Proceedings.
                                                                                               U.S. £PA

     Despite the excellent quality of the Purox fuel,  some communities
in the U.S. that have been considering this system have added at the
back end conventional process technology to produce either ammonia (NH^)
or methanol (CH3OH).   Unfortunately,  the technical  and economic viability
of running such a process on this gas stream remains uncertain.

Liquid Fuel - Occidental  Flash Pyrolysis System

     Process Description.  The Occidental Process (Figure 14) utilizes
two stages of shredding,  air classification, magnetic  separation, drying,
and screening to produce  fluff RDF for the pyrolyse-r feedstock.  Representing
about 60 percent of the input solid waste, the fluff RDF is fed along with
hot char into a vertical, stainless steel reactor.   The hot char, which is
actually the solid residue remaining  after the pyrolysis reaction, provides
the energy needed to pyrolyze the organic material.   The material exiting
the reactor consists of a mixture of  char and ash and  the pyrolysis gases.
By rapidly cooling the gases before they can completely react, a portion of
the gas is condensed into an oil-like liquid fuel.   Both the remaining gas
and the char are reused within the system.

     In going through the elaborate feedstock preparation steps, a by-product
residual is left which is high in glass and aluminum.   This material  is
processed by froth flotation to recover a non-color sorted glass cullet
and by linear motor-eddy  current cement separators  to  recover the aluminum.

     Product Characteristics.  The fuel  product will  be an oil-like,
chemically complex, organic fluid. The sulfur content will be a good
deal lower than that of even the best residual oils.

     The average heating  value of the pyrolytic "oil"  will be about
(10,500 Btu/lb), compared with 18,000 Btu/lb for typical No. 6 fuel oil.
The lower heating value is due to the fact that pyrolytic oil is lower
in both carbon and hydrogen and containers mcuh more oxygen.  A barrel of
oil derived from the pyrolysis of municipal  waste contains about 76
percent of the heat energy available  from No.  6 oil.

     Pyrolytic oil will be more viscous than a typical residual oil.
However, its fluidity increases more  rapidly with temperature than does
that of No 6 fuel oil. Hence, although it must be pumped at higher
temperatures than are needed to handle heavy fuel oil, it can be atomized
and burned quite well at  240 F.  This is only about 20 F higher than the
atomization temperature for electric  utility fuel oils.

     The San Diego Gas and Electric Company has agreed to purchase the
fuel for use in one of its existing oil-fired steam-electric power
plants.  However, the fuel will first be put through an extensive testing
program to determine its  suitability  and to determine  a price for it.

     Status.  The first prototype plant is currently under construction
in El Cajon, California.   It is being built by San Diego County with
the financial assistance  of a demonstration grant from the U.S. Environmental.
Protection Agency and a subsidy from  Occidental Petroleum.  This 200 ton


                    TO LANDFILL   TO GLASS COMPANY
                                                                                   FINE SHRED
                          MIXED COLOR GLASS
                 Figure 14.  Production of "Oil" from Solid Waste Using the Occidental Process

per day plant was begun  in August,  1975 and  it is expected that plant
start-up will begin in September,  1976.  Several months of start-up
operations will  proceed  a  one year  testing and evaluation program.

      Energy Balance.  An energy balance for  the system is shown in
Figure 15.  Although electricity and some quench oil  is purchased for
the facility, it is assumed in this  analysis that these energy inputs
were  produced within the system using normal  conversion efficiencies
that  would result if the pyrolytic  fuel product was  the prime  energy
source.   From the figure it can be  seen that one pound of solid waste
having a heat value of 5,000 Btu's yield 2050 Btu's  of liquid  fuel, with
the rest being  lost in the residue  and char.   However, when  the 741
Btu's  of energy  needed to  produce the equivalent amount of purchased
energy put into  the system is subtracted, only 1309  Btu's (or  26 percent
of the energy in the original pound  of solid waste)  of fuel  remains
            256 Btu
  436 Btu
              RESIDUE 8 CHAR
              3998 Bfu
           Figure 15. Occidental Petroleum System Energy Balance *
 *This balance was based upon data obtained from:

 Flanagan, B. J., Pyrolysis of Domestic Refuse with Mineral Recovery, in Proceedings; Conversion of
  Refuse to Energy, Montreux, Switzerland, November 3-5, 1975. New York, Institute of Electrical and
  Electronics Engineers, p. 220-225.

 Levy, S., The Conversion of Municipal Solid Waste to a Liquid Fuel by Pyrolysis, in  Proceedings;
  Conversion of Refuse to Energy, Montreux, Switzerland, November 3-5, 1975. New York, Institute of
  Electrical and Electronics Engineers, p. 226-231.

     A conventional boiler using this type of fuel will operate at an
efficiency of 87 percent, so the net amount of energy available from the
original pound of soTid waste, once converted to steam is 1139 Btu's or
23 percent.

                    Biological Gasification Systems

     Anaerobic biological digestion of organic materials is a familiar
and widely used process.  Landfill stabilization, domestic sewage stabi-
lization by septic tanks, or municipal sewage sludge digesters all utilize
the same basic process.  However, it cannot be said that the process is
well understood.  Decomposition of organic materials into methane, water,
and carbon dioxide is the result of the life process of some bacteria which
reside in an obviously complex environment.  Some of the effects of varia-
tions in that environment on the health and productivity of the bacteria
are well known while many others are not.  Even so, the level of knowledge
and the engineering state of the art are such that the anaerobic digestion
of solid waste could be attractive as an energy recovery and waste disposal
method for the relatively near future.  Recent research has greatly expanded
the knowledge about using anaerobic digestion to produce methane from solid

     Anaerobic digestion of wastes requires the action of two types of
bacteria:  the acid formers, which are hardy and very resistant to changes
in their environment, and the methane formers, which are strictly anaerobic,
slow growing, and susceptible to upset.  There are two steps in the digestion
process:  First, the acid formers break down the complex organic materials
into organic acids.  Second, the methane formers feed on these organic
acids to produce methane, carbon dioxide, and water.

     These biological reations are used to convert refuse into methane
in two different types of systems:  landfill gasifiers and biological
reactors.  Ther former is considered "developmental" as it is being pursued
in several prototype operations, but the latter is still "experimental."

Landfill Gasifier

     Project Description.  In California, several landfill operators
are taking advantage of natural phenomena to recover usable methane which
is produced naturally by the decomposing solid waste.  The system employs
a deep (over 200 ft. depth) sanitary landfill with impermeable bottom and
gas permeable (porous) daily cover (Figure 16).  Cells have been allowed
to attain field capacity (saturated with water) and are then capped.  Once
wet, the micro-organisms begin reducing the cellulose in mixed municipal
waste to methane and carbon dioxide.  The landfill is equipped with per-
forated well casings which direct the gas into a gas collection system.

     Project Characteristics.  Gas is primarily methane and carbon
dioxide, but it does contain small amounts of hydrogen sulfide and organic
acids, and the gas stream is saturated with moisture.  As a result, unless
the gas is consumed in equipment specifically designed to utilize digester


                                                        ALTERNATE ROUTE-
                                                        METHANE AND CARBON DIOXIDE
                                                        TO CLEAN UP AND USE
                                GAS COLLECTION
                                TUBE    —J
                                                      GAS WELL
                         Figure 16. Production of Electricity from Landfill Gas

off-gas  (as  in  sewage  treatment plants), it must be dehydrated and  "sweetened"
(the carbon  dioxide  is stripped and the acids removed).  This method  of
energy recovery results in a  fuel  product which can be obtained from  an
existing landfill  and  may be  compatible with utility boilers and  residential
fuel requirements.

     Status.  Pilot  or prototype installations are currently recovering
methane from two  landfills in Los  Angeles, California where both  direct
use in a reciprocating engine-generator set and-sweetening to pipeline
quality for  residential  consumption are being practiced.  Also, a research
study, underway at the landfill in Mountain View, California, is  attempting
to quantify  the various gas recovery parameters so that relaiable technical
and economic surveys can be conducted at other potential sites.

Reactor Gasifiers

     Process Description.  Reactor-based gasification involves the  controlled
introduction of fluff  or wet  process RDF and sewage sludge into a heated,
well mixed,  anaerobic  digester where the micro-organisms reduce the
cellulose in the  solid waste  to methane and carbon dioxide (Figure  17).
The retention time within the reactor will be 5 to 10 days during which the
fastest rate of. decomposition takes place.  It would not be economical  to
build reactors  large enough to hold the material  until it is fully
                                        LIGHT FRACTION OUTPUT
               RESIDUE TO
                         GAS OUTPUT*	
              Figure 17.  Biological Gasification of Solid Waste in Reactors

digested.  Thus, the residue that is removed is not fully digested and
represents about 50 percent of the orginal  input weight.-  Results from
a pilot plant operated in Franklin, Ohio,  indicate that the residue dewaters
easily, and that it contains approximately half of the energy potential
of the input waste.  Using vacuum filters  and mecahnical  presses, it
can probably be dewatered to 55 percent moisture, the same as wet process
fuel.  The residue could then possible by  used as a boiler fuel  in
specially designed boilers.   This use would have to be carefully designed
because the residuel is odorous.

     Status.   The result of laboratory and systems studies indicate
that the technology is promising  and would be economic when the price
of gas rises above $2.00 per million cubic feet.  Since the intrastate
price of natural gas is above that level  in many states today, the process
may prove to be eonomical in the  near future.  However, the technical
feasibility has yet to be proven  at anything above pilot scale experiments.
In addition to the one ton per day gasifier in Franklin,  Ohio, Waste
Management, Inc. is designing a 50 tpd prototype unit for construe tion in
Pompano Beach, Florida, under a contract from the Energy Research and
Development Administration.

     Among the questions remaining to be answered are:  (1.) Is the entire
process economical?  (2) Can the  reactors  operate on mixed municipal solid
waste (people throw out materials such as  pesticides which have the capability
of upsetting a digester and preventing it  from producing gas)?  (3) Is
the existing equipment for mixing the refuse-sludge slurry in the reactors
adequate or is a significant hardware development effort required?

     Energy Balance.  Figure 18 shows the  energy balance for biological
gasification of solid waste mixed with sewage sludge in a reactor.  It can
be seen that only one-third of the energy  in the "as received" solid
waste is recovered as methane gas.  When burned in a boiler having an
efficiency of 85 percent, the net yield is 25 percent.  In this analysis, it
has been assumed that energy required to operate the equipment and heat the
digester was obtained by burning  the solid residuals recovered from the
digester and the front end system.  In addition, recovery of these
residuals adds an additional 633  BTU's of steam per pound of solid waste,
increasing overall system energy yields to 42 -percent.  If the residuals
cannot be used as fuel, and system energy requirements are subtracted
from the methane yield, the net energy yield of the system would be
reduced to 14 percent.

     Product Characterisitics.  Reactor gas is predominantly carbon dioxide
and methane, in almost equal quantities.  The gas has a heat value of about
600 BTU/cu. ft., about 60 percent the value of natural gas.

                         Waste-Fired Gas Turbine Systems

     In gas turbine systems (Figure 19) high pressure gases resulting from
the combustion of solid waste with compressed air are used to drive a gas


                                            CONVERSION LOSSES
                                                 239 Btu  (STEAM)
                                                                 R/C 8
                                                                , STACK

17 F = 33%


Tig- 85%

^ 	 '
1 ! -

71 — 2

                                                 R/C 8 STACK
                                                 2103 Btu
                                                            1402 Btu
878 Bfu
                                                                    Tj        - 17%
                                                                      3 RESIDUE
                Figure 18. Energy Balance for Biological Gasification
"This balance was based upon data obtained from:

Pfeffer, J. T., and J. C. Liebman, Biological Conversion of Organic Refuse to Methane, Semi-Annual
 Progress Report covering period 7/1/74 to 12/31/74, Department of Civil Engineering, University of
 Illinois at Urbana-Champaign. January 1975. p. 64.

Kispert, R. G.,  L. C. Anderson, D. H. Walker, S. E. Sadek, and D. L. Wise, Fuel Gas Production from
 Solid Waste, Semi-Annual Progress Report, Dynatech R/D Company, July 1974. p. 52-58.
turbine.   The only example  of a waste-fired  gas turbine system  is the
CPU-400 under development by the Combustion  Power Company.  In  this system
fluff RDF  is burned in a fluidized  bed furnace (fuel  is burned  in an
expanded bed of stones) which keeps  temperature and excess air  low.  The
resulting  gases are cleaned of fly  ash using inertia!  separators  and
gravel bed filters.   The clean gases,  at temperatures  around  1450 F,
are introduced into a gas turbine-generator  set to produce electricity.

      Status.  Severe difficulties have been  encountered in high  temperature
particulate (dust)  removal.   Additional  problems due  to condensation of
vapor phase "aerosols" in the gases  may prove  to be inherent.   Extensive
R&D programs are now ongoing and, until  they are successfully completed,  the
status of  the system must be considered as experimental.


                                                                                           BAG HOUSE
                                                                       GRAVEL BED FILTER

                   EXHAUST DUCTS
                 TURBINE EXPANDER
                    Figure ] 9. Gas Turbine Generating System Using Refuse as a Fuel (CPU-400)

      Energy Balance.   The primary  energy product in the gas  turbine system
is electricity  (Figure 20).  About 12 percent  of the original  energy
is recovered as electricity.  This number should not be confused with the
yeilds  of the other energy recovery systems, which were calculated on the
basis of steam  recovery, as there  is a substantial energy  loss in converting
steam to electicity.   Thus if the  steam yield  from the Monsanto pyrolysis
system,  for instance,  were converted to electricity, the efficiency would  be
reduced  to about  16 percent, not much better than the yield  for this system.

      In  addition  to the electrical energy recovered from the Brayton cycle,
there is potentially  19.4 percent  more energy  which can be recovered as steam.
This  would require the use of a waste heat boiler to recover energy from the
gases after they  pass  through the  turbine.
                                                                     BOILER, COMBUSTOR
                                                                     a TURBINE

                                                                     R/C 8 STACK
                                                                     2707 8TU
T 44 BTU
                                                         OVERALL 31.7% OF THE
                                                         INPUT ENERGY IS CONVERTED
                                                         INTO USEFUL FORMS
                  Figure 20.  Gas Turbine Energy Balance *
   "This balance was based upon data obtained from:

   CPU-400 Systems Studies and Preliminary  Design, Combustion Power Company, Inc., U.  S.
   Environmental Protection Agency, Office of Research and Development, Cincinnati, Ohio. 72 p.

                                SECTION IV

                        MATERIALS RECOVERY SYSTEMS

     Materials recovery encompasses  methods and procedures for extracting
useful  materials from solid waste for return to the economy.   The
prime objectives in the development  of materials recovery systems are:
(1)  to conserve natural resources and energy;  ('2) to reduce  land
requirements for disposal; (3)  to facilitate the preparation  of refuse
derived fuels for energy recovery systems.

     Materials can be recovered through source  separation, hand sorting,
or mechanical separation.   This report addresses only mechanical
separation.   Mechanical separation methods capable of segregating
solid waste into valuable components have developed, based on techniques
use in the mining and paper industries.  These  methods are aimed at
minimizing the level of impurities in recovered products so that
maximum dollar value can be obtained for the recovered material.
Material recovery systems have  concentrated on  the reclamation of
fiber or paper (the most abundant component in  solid waste);  magnetic
metals (the most easily extractable); aluminum  (the most highly
valued); and glass (the most difficult to extract).

     Material recovery components are often combined with energy
recovery systems.  These systems are designed to serve as total
recovery plants.  Section III of this report describes systems which
convert part of the solid waste into a fuel product.  The following
subsections describe some of the subsystems used in these solid waste
disposal/energy recovery systems to  recover valuable resources.

                           Paper Fiber Recovery

     Paper fiber recovery processes  use either  wet or dry primary
separation of fibers from mixed municipal waste.  The initial separation
steps are similar to those employed  in dry and  wet RDF production
facilities.  In fact, it may be practical in some situations  to
establish both a fuel and a fiber market for the paper so that the
actual end use of the product can change in response to changes in
market demand (value).

Wet Processing Concept - Fiber Recovery

     The major components of a wet processing system are described in
Section III.  The fiber recovery portion of the facility is described

     Process Description.  Figure 21 is a flow chart of the components
of the fiber recovery subsystem.  The feedstock to the fiber recovery
process is the same material as taken to the dewatering presses
in a wet fuel processing system.  The hydrapulped  solid waste  is


                                                                                 I     I RECYCLE WATER TANK
                                                                               —•"<	'
                                                                           TO RECOVERY OF.
                                                                             SMALL FERROUS METALS
                                                                             GLASS (BY COLOR)

                                                                             (SEE FIGURE  26)
                       Figure 21.  Wet Process Fiber Recovery System

centrifugally separated  and light fraction taken to  fiber recovery.
The first step in the  beneficiation process is to remove all large
particles from the slurry.   This is accomplished by  screening.  All
particles greater than 1/16 inch diameter, including  the plastic films,
are removed.   The fibrous  slurry is then  passed through  a series of  high
efficiency centrifugal cleaners and screens which remove grit.  The
material  exiting the cleaners and screens is recovered fiber.  This
material  can  be washed and  dewatered prior to shipment for use in a
manufacturing process  or for further upgrading (cleaning and removal
of shorter fibers).

     The  economic viability of fiber upgrading processes is determined
by the market for the  recovered products.   Generally, long-term
contracts must be secured and the price of the upgraded  fiber must
be sufficiently higher than unbeneficiated fiber to warrant the extra

     Figure 22 presents  a mass balance for the recovery  of paper fiber
using wet processing.  About 20 percent by weight (dry)  of the incoming
municipal  solid waste  is recovered as marketable fiber.   This represents
approximately 50 percent of the paper fiber content of the solid waste
on a dry  weight basis.
  JUNK i   I3LB

        3.2 GAL.
                                                              10LB RECOVERED FIBER

                                                                 (•*• 10 LB WATER )
                           TO GLASS RECOVERY
                            REJECTS- 12 LB
                            (GLASS, STONES,
                             ALUMINUM, GRIT, ETC.)
                             REJECTS FOR
                             DISPOSAL  38 LB
                           X (•» 38 LB WATER)
          Figure 22. Mass Balance for Wet Process Fiber Recovery

 "This balance was based upon data obtained from:                                 v

 Wittmann, T. J., et. al., A Technical, Environmental and Economic Evaluation of the "Wet Processing
  System for the Recovery and  Disposal of Municipal  Solid Waste", Final Report SW-109c, U. S.
  Environmental Protection Agency, 1975. 217 p.

     Status.  The fiber recovery process was developed by the Black-
Clawson Company and has been demonstrated with a 150 ton per day
plant built in Franklin, Ohio.  This plant has been in continuous
operation since 1971.  Fiber recovered at the plant is currently
being sold to a manufacturer of asphalt impregnated roofing shingles.
However, recent combustion tests have established a market for the
fiber as a fuel and henceforth the fiber will be sold to the most
lucrative of the two markets.

     Although the wet fiber recovery process has been successfully
demonstrated, the large fluctuation which occurs in the paper fiber
market, and the fact that the fiber is suitable for only low grade
uses has limited the systems economic viability.  In fact, as discussed
in Section III Black-Clawson is currently promoting the use of its
wet pulped fuel recovery system instead of its fiber recovery system.

     Product Characteristics.  The paper fiber recovery at Franklin is
of fairly low quality.  It is shipped to its market via a short pipeline
as a slurry containing 4 percent solids.  The major contaminent impacting
on its quality is oil and grease.  Microbial organisms which survive the
pulping and recovery processes are also a problem in that they severely
restrict the "shelf-life" of the fibre and require that its end use
include a heat treating step where the organisms are killed.

Dry Processing Concept - Paper Recovery

     Process Description.  Another technique for paper recovery is
displayed in Figure 23.  The concept involves the recovery of paper
using a series of air classifiers and rotary screens to remove and
upgrade the paper fraction from shredded solid waste.   The paper
fraction removed by air classification is baled and either marketed
in this form or further processed using a wet processing system similar
to the wet process fiber recovery system.

     As illustrated in Figure 23, the solid waste is first shredded
followed by the removal of magnetics.  An air classifier separates
the paper and plastic from the remaining stream.  Further air
classifying removes the plastic fraction from the paper/plastic

     When wet processing is used as the final clean up step, the paper/
plastic fraction is charged into hydrapulpers and converted into a
paper-water slurry.  Plastics float on the surface of the hydrapulper
and are removed at regular intervals.  Heavy foreign matter and more
plastics are removed by screening.

     The fiber-rich pulp is discharged from the pulper to a hydracyclone
to remove small particulate matter (grit).  The cleaned slurry is pumped
to a prethickener where a large portion of the water is removed for
recycling to the pulper.  This thickened material is conveyed to a


                     TO ALUMINUM*-
                                                                              TO PLASTICS RECOVERY
                   FLAIL MILL

                              DRUM SEPARATOR
II ^1
                    TO FIBER USE
                           Figure 23.  Dry Process Paper and Materials Recovery

dewatering press where the material is concentrated to approximately
38 percent solids and additional water is recycled to the pulper.
The fibrous material is then processed in a refiner (mixing, grinding,
and steaming steps) to remove unwanted paraffins and tar residues from
the fiber product.

     Status.  This process has been developed by the Cecchini Company
of Rome, Italy.  Cecchini presently operates three plants in Italy.
Paper from these plants is used, along with straw, to make a low
grade paperboard.  No tests have been conducted to determine if such
a product would be marketable in this country.

     Product Characteristics.  Like the wet recovery system fiber, the
paper recovered in the dry separation system is of low quality, and as
a result, has limited marketability.  It's major contaminant is plastics.
Product yields are lower in this process as substantial  amounts of paper
are lost in the air classifying and screening operations.  It is estimated
that approximately 23 percent of the input paper is recovered as
marketable fiber.


     Composting of municipal refuse is a method of converting the organic
portion of mixed solid waste into a soil conditioner.   This conversion
is accomplished by a well known biological process called aerobic
digestion, the decomposition of organic materials by microorganisms
which require air to live.  The humus which results from composted
refuse can improve the tilth and moisture retention characteristics
of poor soils.  Clays are only temporarily improved by the addition of
humus, but sandy soils can benefit substantially, especially in dry
climates.  Composting of municipal refuse has been practiced in Europe
where intensive agriculture by speciality farmers and other small
landholders is carried out close to large towns and cities.

     Three basic methods of composting are distinguishable:  windrowing -
digesting of the material in open stacks laid on the ground; tilling
the undigested organics into soil containing mature compost; and
completely mechanized industrial composting plants.

     The first two processes require large amounts of land, a condition
which rarely exists near today's American cities.  The third requires
mechanical equipment.  The windrowing process can require as much as
30 days to achieve a mature compost, while the mechanical process
can go to completion in two to ten days.  (In most of the United
States, 10 days are required because of the high paper fraction in mixed
municipal waste.)

     Composting processes require moisture addition and  mixing to
provide adequate aeration of the material.  In addition, efficient
composting requires that the organic components in the solid waste


be reduced to small particle sizes and that as much as possible of the
inert materials be removed from the waste stream prior to processing.
The size reduction and inerts cleanup requirements for composting are
almost identical to the processing requirements for production of fluff
RDF.  The same equipment can be used for both.

     Since similar processing is required for the preparation of refuse
for composting and RDF, and since RDF is expected to be more readily
marketable than compost in an urban economy (near the waste generation
centers), it is unlikely that composting will be able to compete with
energy recovery as a solid waste management tool.  Furthermore, composted
refuse is a very low grade fertilizer which cannot compete with available
chemical fertilizers on American farms.   Finally, the soil in very
few areas of the United States is in need of the type of soil conditioning
offered by humus.  The high processing costs (whether in terms of land
or equipment) and the lack of a suitable market indicates that the
composting of municipal solid waste is not a promising method of urban
solid waste management.  The possible exception is its use in sections
of the country where sandy soils exist,  solid fuel combustion is
economically prohibitive, and a strong,  long-term market for humus

                          Ferrous Metals Recovery

     Process Description.  Ferrous metal reclamation is a subsystem
which can be incorporated into almost all, energy and materials recovery
systems.  The technology for extracting  ferrous metals is based on
magnetic attraction of ferrous materials and is readily available.

     Magnetic separation of ferrous metals from municipal solid waste
generally follows the first stage of shredding.  In many sophisticated
resource recovery systems, magnetic separators are also employed
later in the system to recover any ferrous metal  that was initially
missed.  Particle size does not appear to be critical  since existing
equipment can easily remove most ferrous objects which appear in
urban solid waste.  Bulky items such as  appliances can be either
manually sorted or shredded prior to magnetic separation.  Heavy
ferrous objects, such as motor casings,  are generally manually separated
in order to protect the size reduction equipment.

     Two broad classes of magnetic separators are used in solid waste
processing (Figure 24):  suspended types and head pully types.  Suspended
type separators, positioned over solid waste feed conveyors, are
used to remove ferrous metals from solid waste which may or may not
have been shredded.  The recovered ferrous metal  is contaminated with
paper so that air scalping or secondary magnetic separation is needed
to produce a marketable fraction.  Head  pully type separators are generally
employed as a means of secondary ferrous separation.

                        BELT  MAGNET
                                                       AIR KNIFE-
                                                       PAPER BACK TO
                                                                 HEAD PULLEY
                                                                       PAPER a
                                                                       PLASTIC FILMS
                        Figure 24. Magnetic Separator Configuration

     The suspended magnetic separator lifts ferrous metals from the
waste and deposits them on a separate belt.  The head pully causes
ferrous metals to follow the conveyor around the head and drop behind
the solid waste stream.

     Product Considerations.  There are three principal  uses of ferrous
scrap in the United States today:  detinning, steel production, copper
precipitation.  Each of these industries have different physical requirements
and contaminant restrictions for ferrous scrap.   These markets are
discussed in the Markets section of this guide (SW-157.3).  The actual,
or most likely market for ferrous metal  recovered from a proposed plant
should be determined before the plant is designed so that the plant can
be designed to produce a ferrous product that will  meet the specifications
of the market.

     Recovery rates of 90 to 97 percent of the ferrous material in the
waste stream are possible.

     Status.  The technology of ferrous  metals separation and reclamation
is proven and has been demonstrated in numerous  areas.  Magnetic separation
is being used in almost all operating and proposed  energy and material
recovery systems.

                    Glass and Aluminum Recovery  Systems

     Recovery of glass and aluminum from mixed municipal  solid waste
would occur after the waste has been processed to remove the bulk of
the organic or combustible waste and ferrous metals.   Thus, equipment to
recover glass or aluminum would normally be preceded by  one or more
stages of shredding, air classification, magnetic separation and screening.
Thus, glass and aluminum recovery can be viewed  as  a supplement to other
processing and recovery systems.  The separation equipment receives a
mostly nonorganic concentrate containing primarily  glass, aluminum, and
nonferrous metals, as well as stones and some leftover ferrous metals.
This stream is often referred to as "heavies".  Some residual  organics
including food, paper, rubber, plastic,  and leather are  still  in the

     Since separation of one of the desired components (e.g. aluminum)
leaves a component with a heavy concentration of the other (e.g. glass),
glass and aluminum recovery are often viewed as  joint recovery operations.
However, recovery of only one or the other of the components is clearly

     Aluminum is difficult to extract because it has no  unique physical
characteristic which can be used to easily isolate  it from the waste
stream, and because it is a minor constituent (generally less than one
percent of municipal solid waste).   It's high value as scrap (approximately
300 per ton) however, makes it a potential  recovery target.


     Glass, on the other hand, has a relatively low scrap value but
because it represents a much larger percentage of the waste stream
(about 9 percent) the value of the glass and the aluminum in a ton of
solid waste are nearly equal.  The major problem in recovering glass
is that stones and ceramics are not readily separable from glass and
these materials are a major contaminant in the manufacture of glass.
Thus, producing a product which can meet the rigid quality standards
specified by the glass industry is difficult.

     Before describing the glass and aluminum recovery systems presently
under development it will be helpful to review some of the unit processes
which are used in these systems.

     -  Heavy Media Separation.  In this process a water suspension
        of finely divided particles of heavy minerals (e.g. magnetite
        or ferrosilicon) is used to create a fluid having a specific
        density which will cause the material being fed to it to
        split into "sink" and "float" fractions depending upon the
        specific gravities of the particles in the feed.  Multiple
        separations can be made by using several stages or cells,
        each at different specific gravities.

     -  Eddy Current Separation.  This is a dry process for separating
        aluminum and other nonferrous metal conductors from non-
        conducting materials.  In these devices an electrical  current
        is imposed on a fixed linear motor located beneath a moving
        belt.  Metal conductors passing through the magnetic field
        created by the linear motors are subject to an induced (Eddy)
        current which opposes the field created by the linear motor.
        The opposing force is strong enough to knock the conductor
        off the belt.  Non-conductors pass over the linear motors

        Combustion Power Company of Menlo Park, California, and
        Occidental Research (formally Garrett Research) of La Verne,
        California, and the Raytheon Company have developed prototype
        aluminum spearation systems using eddy currents.  Systems
        of this type are reportedly under development that will
        include the separation of other nonferrous metals from

     -  Jigging.  This mineral processing technique, is used to
        separate materials of different densities.  Water is pulsed
        through a screen causing material fed onto the screen to
        separate.  The lighter, material is floated off leaving
        the heavier material at the base of the jig.  Jigs have been
        used in laboratory and pilot scale trials for separation of
        aluminum from mixed nonferrous metals.

     -  Electrostatic Separation.   This method for dry nonferrous
        metal  separation is based  on differences in the conductivity
        of materials.  As feed material enter on electrostatic field,
        particles become charged and fall  on a rotating drum.   Con-
        ductors immediately lose their charge on the grounded  drum and
        fall  from it while non-conductors  retain a surface charge and
        adhere to the drum.

     -  Optical Sorting.  Electronic sorting machines are used to
        optically separate 1/4 inch to 3/4" inch diameter glass by
        color.  Glass cullet is fed from a hopper onto a vibrating
        feeder (Figure 25).  A uniform feed of particles is led to
        a grooved belt conveyor which transports pieces in single
        file to a separation chamber.   Here two photo cells (one
        on each side) view the glass.   A color plate is situated
        opposite the photocell  to  provide  a standard against which
        deviations in reflectivity of the  glass are measured.   Those
        particles within a certain range of reflectivity cause a
        voltage change in the photocells which in turn triggers a
        short blast of compressed  air which deflects the particle
        from the main stream.  This equipment can be set up to
        separate transparent particles (glass) from opaque particles
        (stones and ceramics),  to  separate clear glass from colored
        glass (amber and green), or possibly, to separate green
        glass from amber glass.

     -  Froth Flotation.  This  is  a standard mineral processing technique
        being adapted to glass  separation).   Froth flotation is
        accomplished when an air bubble is attached to a selected
        particle having hydrophobic surface characteristics.   This
        desirable surface property is usually achieved by "conditioning"
        the particle using a reagent prior to entering the flotation

        Following air bubble attachment, the floatable glass particles
        are buoyed to the surface  to form  a froth which can then be
        removed by skimmers.  Rotors are used to circulate the glass
        rich slurry and to provide good air-solids mixing.   To achieve
        the required residence time, flotation cells are usually
        arranged in series with adjacent cells separated by baffles
        to reduce "pulp short circuiting."

     There are a number of possible configuarations of these unit processes
in combination with grinding and screening to make up a complete recovery
module.  Two such systems are described below.

Black Clawson System

     Process Description.  The first flow  scheme is in operation in
Franklin, Ohio, at the Black Clawson fiber recovery plant.   The feed


                FEED BELT
                           SEPARATED PRODUCTS
    Figure 25.  The Sortex optical sorter is used to color sort glass particles.
to this system  is the heavy inorganic fraction (glass, nonferrous  metals,
stones and small amounts of ferrous metals and organics) which drops
out of the wet  cyclone (see Figure 21).  The system as it is currently
laid out is shown in Figure 26.   Heavy material  from the cyclone is
mechanically dewatered prior to  entering the surge storage bin.   From
the bin the material is placed on a vibrating screen and the fines and

                                                                                                                HIGH TENSION
                                                                                                                ELECTROSTATIC SEPARATOR
                                                                                                                                OPTICAL SORTERS
                                                                                                                            STONES a CERAMIC
                                                                                                                   1	NON FERROUS METALS
                                           Figure 26.  Wet Processs Glass Recovery System

and some dirt with organic residue is washed off; the fines being
arbitrarily defined as anything less than 1/4 inch.  This undersize
material will not be color sorted or recovered in any way, and it
is sent to the landfill.

     After the screening, the material is magnetically scalped to remove
ferrous metals, and is then conveyed to the heavy media separation unit.
The heavy media separation unit is held at a specific gravity of 2.0
in order to remove any heavy organic materials, specifically plastics,
that have slipped through the liquid cyclone in the main system.
All the floated material is returned to the main plant to be burned
(it would be used as a fuel in a fuel recovery system).  The sink
material, that is, the material that has a specific gravity greater
than 2.0, is sent on to the jigging operation for separation of glass
from nonferrous metals - mainly aluminum.

     The jigging operation, as set up at the Franklin site, has three
output streams - the lightweight, mostly aluminum can-type stock; the
medium fraction which is mostly glass; and a very hea^y fraction,
composed generally of cast metals, such as brass keys, coins,  cast
aluminum, cast zinc, or lead-form material.  With the feed material  held
for the proper residence time within the jigging operation, good
concentrates of aluminum, glass and heavy metal fractions can  be
obtained.  The glass fraction is conveyed from the jigging operation
to the rotary kiln dryer to get rid of the excess surface water.

     The glass fraction is then carried by a conveyor to the electrostatic
separation unit for removal of any remaining metals.

     Material which can be made to carry a charge is pulled out of
the glass rich stream.  Some natural stone, residual cast metal materials
and any residual aluminum can stock is thus removed.  The use  of this
particular device has proved to be very effective for handling materials
ranging in size from 1/4 inch to 1 inch.

     The glass fraction coming from the high tension electrostatic
device is then transported by bucket elevators into hoppers which
feed v-shaped belts for the separation of stones and ceramics  from
the glass fraction by use of a transparency device.  The transparency
device is a relatively new addition to the processing line at  Franklin
and is based on the need to remove an extremely high incedence of
ceramic or refractory materials found in the glass fraction.  These
refractory materials are unacceptable in the manufacture of glass
containers since their presence causes imperfections in the glass
container which destroy the integrity of the jar or bottle.  The
material, once it has been transparency sorted, is then passed
on to a color sorter.

     Status and Product Characteristics.   In a previous study  at
Franklin, the glass composition was segregated into flint, amber


and green glass.   However,  experimentation within the industry determined
that a triple color sorting was not necessary,  and that a flint, non-
flint, (amber and green)  separation would be sufficient.

     While the process appears to satisfactorily sort the glass by
color, achieving  high recovery rates and an acceptable product appear to
be contradictory  goals.   Specifications commonly used by the glass
industry require  that the cullet contain a maximum of two stones
per 100 pounds of cullet.  As  presently operating, the pilot plant is
producing a much  lower quality product.  Extensive modifications and
tests are being undertaken  to  remedy the problem.  However,  at the
present times, color sorting is "developmental" technology.

The Occidental Research  Corporation System

     Process Description.  The Occidental  Research Corporation (ORC) has
constructed a pilot glass and  aluminum recovery plant which  incorporates
froth floatation  for glass  recovery and eddy current separation of
aluminum (Figure  27).

     The material fed to  this  plant consists of municipal solid waste
that has been shredded to a particle size of 1  inch.  The material,
after shredding,  has had  most  of the magnetic metals removed and much of
the organic matter has been removed by air classification.   As a result
of this pre-processing,  the feed material  largely consists of glass,
aluminum, rocks bones, dirt, some magnetic metals, some heavy organics
and other inorganic matter.

     The material entering  the system flows into a trommel which is a
large rotating cylindrical  screen.   The large material, which contains
much of the aluminum, passes through the trommel, is conveyed to a
magnetic separate for "tramp"  ferrous metal recovery, and then to the
aluminum separator.  Here,  a linear induction motor, powered by an
alternator generates a force field which acts upon the pieces of aluminum.
The aluminum is very rapidly deflected to the side of the conveyor belt
and is collected.

     The small material  stream which falls through the trommel screen
openings and is composed  of small dense particles, largely glass, is
conveyed to a wet type spiral, classifier.  Here the material receives
its first cleaning and the  few light organics are removed.   The partially
cleansed material then flows by gravity into a  rod mill for  size reduction.
This sized fraction is pumped  through a cyclone and screen where the
large-sized non-glass material (rubber, plastic, etc.) is removed.  The
contaminated glass is sized to greater than 200 mesh in a classifier
then flows to a conditioning tank where a proprietary ORC reagent called
"SiLECT" is added.  The  "conditioned" glass is  then sent to  a series of
flotation cells called "roughers", "cleaners" and "recleaners".  In the
froth flotation cells, the  pure glass selectively attaches to bubbles.
and floats to the top of  the cells where it is  skimmed off,  collected,
and sent to a final dewatering classifier.  The product glass is then
dried and shipped to market.  Rejects from the  "roughers" are passed
through "scavengers," dewatered, and then discharged as tailings.


FEED  	1
       TO VACUUM
MAGNET    v-~~ ~^    REJECTS

                                                                                            - ADDITION OF
                                                                                            "SILECT" REAGENT
                              METALS AND*
                                                                                      CLASSIFIER "C"
     Figure 27.  The Occidential Research Corporation has set up a glass and aluminum recovery pilot plant
                in LaVerne, California utilizing this flow scheme.

     Undersize material  from the classifier is further processed in a
cyclone and screen *  thickener tank and vacuum filter.   Water used in the
process is filtered  and  treated for reuse.

     Status.  The first  full-scale test of  this system will  be incorporated
in the Occidental Flash  Pyrolysis plant now under construction in San
Diego County, California.   Until full  scale, continuous operational
experience is obtained and market acceptance of the non-color-sorted
cullet has been demonstrated, froth flotation must be  classified as

                                 SECTION V

                               READING LIST


  *McEwen, L. B.  A nationwide survey of resource recovery activities.
     Environmental Protection Publication SW-142.1.   Washington, U.S.
     Environmental Protection Agency.  (In press.)

  *U.S. Environmental Protection Agency, Office of Solid Waste Management
     Programs.  Resource recovery and waste reduction; third report to
     Congress.  Environmental Protection Publication SW-161.  Washington,
     U.S.  Government Printing Office, 1975.  96 p.

  *U.S. Environmental Protection Agency, Office of Solid Waste Management
     Programs.  Decision-makers guide in solid waste management.  Environmental
     Protection Publication SW-500.  Washington, U.S.  Government Printing
     Office, 1976.  158 p.

  *Smith,  F. A.  Comparative estimates of post-consumer solid waste..
     Environmental Protection Publication SW-148.  Washington, U.S.
     Environmental Protection Agency, May 1975.  18 p.

   Parkhurst, J. D.  Report on status of technology in recovery of
     resources from solid wastes.  [Whittier] , County Sanitation Districts
     of Los Angeles, California,  January 13,  1976 .  198 p., app.

Energy Recovery

   Conference papers; CRE, Conversion of Refuse to Energy; 1st International
     Conference and Technical Exhibition, Montreux,  Switzerland, Nov. 3-5,  1975.
     IEEE  catalog no. 75CH1008-2 CRE.   DPiscataway,  N. JJ ,  Institute of
     Electrical and Electronics Engineers.  615p.

   From Waste to Resource Through Processing;  Proceedings; 1976 National
     Waste Processing Conference, Boston, May 23-26, 1976.  New York,
     American Society of Mechanical Engineers.  585 p.

  *McEwen, L. B., and S. J. Levy.  Can Nashville's story be  placed in
     perspective?  Solid Wastes Management/Refuse Removal Journal,  19(8):
     24, 28-39, 58, 60, August 1976.

   Roberts, R. M., et. al.  Envirogenics Company].  Systems  evaluation  of
     refuse as a low sulfur fuel.  Washington, U.S.  Environmental  Protection
     Agency, 1971.  2 v.  (Distributed by National Technical Information
     Service, Springfield, VA, as PB-209 271  - PB-209 272.)


  +Levy, S. J.  A review of the status of pyrolysis as a means of
     recovering energy from municipal  solid  waste.   Presented at 3d
     U.S.  - Japan Conference on Solid  Waste  Management, Tokyo,
     May 12-14, 1976.   Washington, U.S Environmental  Protection Agency,
     Office of Solid Waste Management  Programs.   29 p.

  *Sussman, D. B.   Baltimore demonstrates gas pyrolysis;  resource
     recovery from solid waste.  Environmental  Protection Publication
     SW-75d.i.  Washington, U.S.  Government  Printing  Office, 1975.   24 p.

   Davidson, P. E.   Slagging pyrolysis solid waste  conversion.  Engineering
     Digest. 21(7):31-34,  August 1975.

   Anderson, J. E.   The oxygen refuse  converter - a system for producing
     fuel  gas, oil,  molten metal  and slag from refuse.  J_n Resource
     Recovery Thru Incineration;  Proceedings; 1974  National  Incinerator
     Conference, Miami, Florida,  May 12-15,  1974.  New York, American
     Society of Mechanical  Engineers,   p. 337-357.

  *Levy, S. J.  San  Diego County demonstrates pyrolysis of solid waste
     to recover liquid fuel, metals, and  glass.   Environmental Protection
     Publication SW-80d.2.   Washington, U.S. Government Printing Office,
     1975,  27 p.

   Preston, G. T.   Resource recovery and  flash  pyrolysis  of municipal
     refuse.  J_n_ Clean Fuels from Biomass, Sewage,  Urban, Refuse and
     Agricultural  Wastes Symposium,  Orlando, Florida,  Jan.  27-30, 1976.
     Chicago,  Institute of Gas Technology,   p.  89-114.

  *Hitte,  S. J.  Anaerobic digestion of solid waste and sewage sludge
     to methane.  Environmental Protection Publication  SW-159.   [Washington],
     U.S.  Environmental Protection Agency, July 1975.   13 p.

  Pfeffer,  J.  T.   University of Illino'is, Department  of  Civil Engineering .
     Reclamation of  energy from organic waste.   Washington,  U.S.  Environmental
     Protection Agency, March 1974.  143  p.   (Distributed by National
     Technical Information Service,  Springfield, VA,  as PB-231 176.)

Materials  Recovery

  *Arella,  D.  G.  Recovering resources from  solid waste using wet-processing;
     EPA's  Franklin, Ohio,  demonstration  project.  Environmental  Protection
     Publication SW-74d.  Washington,  U.S. Government  Printing Office,
     1974.   26 p.

   Systems  Technology Corporation.  A  technical, environmental and
     economic evaluation of the "wet processing system for the recovery
     and disposal  of municipal solid waste."  Environmental  Protection
     Publication SW-109c.   U.S. Environmental Protection  Agency,  1975.  223 p.
     (Distributed by National  Technical  Information Service, Springfield, VA,
     as PB-245 674).


  +Levy, S.  J.  Materials recovery from post-consumer solid waste.
     Presented at 3d U.S.-Japan Conference on Solid Waste Management,
     Tokyo,  May 12-14, 1976.   Washington,  U.S.  Environmental  Protection
     Agency.  29 p.

   Morey, B., J. P.  Cummings,  and T.  D.  Griffin.   Recovery of small
     metal  particles from nonmetals using  an eddy current separator  -
     experience at Franklin,  Ohio.  Presented at 104th Annual  Meeting.
     American Institute of Mining, Metallurgical  and Petroleum Engineers,
     New York City,  February  16-20, 1975.   11 p.

   Campbell, J. A.  Electromagnetic separation of aluminum and nonferrous
     metals.  Presented at 103d Annual  meeting,  American Institute of
     Mining, Matallurgical and Petroleum Engineers, Dallas,
     February 24-28, 1974.  17 p.

   Non-ferrous metals recovery...conserving a valuable resource.  NCRR
     Bulletin. 5(3):67-72, Summer 1975.

   McChesney, R., and V. R. Degner.  Hydraulic,  heavy media,  and  froth
     flotation processes applied to reocvery of metals and glass  from
     municipal solid waste streams.  Presented at 78th National Meeting,
     American Institute of Chemical Engineers,  Salt Lake City,
     August  18-21, 1974.  27  p.

   Samtur,  H. R. Glass recycling and reuse.  IES Report 17.   Madison,
     University of Wisconsin,  Institute for Environmental  Studies,
     March  1974.  100 p.

   Cummings, J. P.  Glass and  non-ferrous  metal  recovery subsystem at
     Franklin, Ohio - final report.  ln_ Proceedings; 5th Mineral  Waste
     Utilization Symposium, Chicago,  April 13-14, 1976.   Chicago  IIT
     Research Institute,  p.  175-183.
     *Available from:  Solid Waste Information Control  Section,  U.S.
Environmental Protection Agency, Cincinnati, Ohio  45268.

     +Available from:  Resource Recovery Division, Office of Solid
Waste Management Porgrams, U.S. Environmental Protection Agency,
Washington, D.C.  20460.