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ACKNOWLEDGEMENTS
CITY OF LOS ANGELES
Evaluation of Alternative Solid Waste
Processing Technologies Report
MAYORAntonio R. Villaraigosa
CITY COUNCILMEMBERS
Ed P. Reyes CD 1 Wendy Greuel CD 2
Dennis P. Zine CD 3 Tom LaBonge CD 4
Jack Weiss CD 5 Tony Cardenas CD 6Alex Padilla CD 7 Bernard Parks CD 8
Jan Perry CD 9 Vacant CD 10
Bill Rosendahl CD 11 Greig Smith CD 12
Eric Garcetti CD 13 Vacant CD 14
Janice Hahn CD 15
BOARD OF PUBLIC WORKS
Cynthia M. Ruiz, President
David Sickler, Vice President
Paula A. Daniels, President Pro-Tempore
Yolanda Fuentes
Valerie Lynne Shaw
BUREAU OF SANITATION
Rita L. Robinson, Director Joseph E. Mundine, Executive Officer
Enrique C. Zaldivar, P.E. Assistant Director Varouj S. Abkian, P.E. Assistant Director
Traci J. Minamide, P.E. Assistant Director
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ACKNOWLEDGEMENTS
Special thanks to Ms. Rita L. Robinson and Mr. Enrique C. Zaldivar for their valuableadvice. This report could not have been completed without the assistance and collaboration
of many dedicated members of the Bureau of Sanitation, Solid Resources Support Services
Division, including:
Alex E. Helou
Carl L. Haase
Richard F.WozniakJavier L. Polanco
Kim Tran
Miguel A. Zermeno
OTHER CITY DEPARTMENTS AND DIVISIONS:
Bureau of Sanitation:Solid Resources Processing & Construction Division
Solid Resources Citywide Recycling Division
Solid Resources Valley Collection Division
Solid Resources South Collection Division
Department of Water and Power
CONSULTANTS
URS Corporation
Alfonso Rodriguez
Dan Predpall
Shapoor Hamid
JDMT, Inc.
Michael Theroux
Sheri Eiker-Wiles & Associates
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TABLE OF CONTENTS
Section Page
EXECUTIVE SUMMARY ...............................................................................................ES-1
1.0 IDENTIFY ALTERNATIVE MSW PROCESSING TECHNOLOGIES .............1-1
1.1 INTRODUCTION ............................................................................................... 1-1
1.2 BUSINESS OBJECTIVES .................................................................................. 1-21.3 EVALUATION METHODOLOGY ................................................................... 1-2
1.4 ALTERNATIVE MSW PROCESSING TECHNOLOGIES .............................. 1-4
1.5 LIST OF TECHNOLOGY SUPPLIERS............................................................. 1-4
2.0 CHARACTERIZE ALTERNATIVE MSW PROCESSING
TECHNOLOGIES...................................................................................................... 2-1
2.1 INTRODUCTION ............................................................................................... 2-1
2.2 THERMAL PROCESSING TECHNOLOGIES ................................................. 2-3
2.2.1 Advanced Thermal Recycling.................................................................. 2-5
2.2.2 Pyrolysis................................................................................................... 2-8
2.2.3 Gasification............................................................................................ 2-15
2.2.4 Plasma Arc Gasification ........................................................................ 2-21
2.3 PHYSICAL PROCESSING TECHNOLOGIES ............................................... 2-24
2.3.1 Refuse Derived Fuel .............................................................................. 2-24
2.3.2 MSW Handling Processes...................................................................... 2-26
2.4 BIOLOGICAL AND CHEMICAL PROCESSING TECHNOLOGIES........... 2-29
2.4.1 Introduction............................................................................................ 2-29
2.4.2 Anaerobic Digestion .............................................................................. 2-31
2.4.3 Ethanol Production................................................................................. 2-34
2.4.4 Biodiesel ................................................................................................ 2-36
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Section Page
3.2.1 Toward Standardized Permitting and Enforcement................................. 3-2
3.2.2 Renewable Energy Generation ................................................................ 3-3
3.2.3 Life Cycle and Market Assessment ......................................................... 3-5
3.2.4 Current Regulatory Concerns .................................................................. 3-8
3.2.5 Current Status of Definitions ................................................................... 3-9
3.3 REGULATIONS AFFECTING ALTERNATIVE TECHNOLOGY
DEVELOPMENT.............................................................................................. 3-11
3.3.1 Local, State, and Federal Interaction ..................................................... 3-11
3.3.2 California Energy Commission Regulations ......................................... 3-15
3.3.3 California Integrated Waste Management Board Regulations .............. 3-15
3.3.4 Summary of Permitting Requirements................................................... 3-15
3.4 REGULATIONS AFFECTING COMPOST MARKETABILITY................... 3-16
3.4.1 MSW Feedstock Variability .................................................................. 3-17
3.4.2 Process Control Challenges ................................................................... 3-18
3.4.3 Voluntary Quality Control for Compost ................................................ 3-19
3.4.4 Regulatory Oversight Federal ............................................................. 3-203.4.5 Regulatory Oversight State ................................................................. 3-21
3.4.6 Summary ................................................................................................ 3-24
4.0 SCREENING OF ALTERNATIVE MSW PROCESSING TECHNOLOGIES .. 4-1
4.1 INTRODUCTION ............................................................................................... 4-1
4.2 TECHNOLOGY SCREENING CRITERIA ....................................................... 4-14.3 ALTERNATIVE MSW PROCESSING TECHNOLOGY SCREENING.......... 4-2
4.4 WASTE SAMPLING PROGRAM...................................................................... 4-4
4.5 TECHNOLOGY SUPPLIER SCREENING CRITERIA.................................... 4-5
4.6 TECHNOLOGY SUPPLIER SURVEY.............................................................. 4-6
4.7 SCREENED TECHNOLOGY SUPPLIERS....................................................... 4-7
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TABLE OF CONTENTS
Section Page
8.1 SUMMARY OF KEY FINDINGS...................................................................... 8-1
8.2 CONCLUSIONS.................................................................................................. 8-1
8.3 RECOMMENDATIONS..................................................................................... 8-6
8.3.1 Public Outreach........................................................................................ 8-6
8.3.2 Develop a Short List of Suppliers............................................................ 8-88.3.3 Initial Siting Study ................................................................................... 8-8
8.3.4 Preparation of Request for Proposal and Select Preferred Supplier ........ 8-8
8.3.5 Conduct Facility Permitting and Conceptual Design............................... 8-8
8.3.6 Detailed Design and Construction ........................................................... 8-8
GLOSSARY
List of Tables Page
Table ES-1 Key Findings...................................................................................................ES-4
Table ES-2 Recommended Activities for MSW Processing Facility Development
for the City of Los Angeles.............................................................................ES-9
Table 1-1 Classification of MSW Processing Technologies............................................. 1-5
Table 3-1 Summary of Permits Required for a New Solid Waste Processing Facility..... 3-1
Table 4-1 List of Alternative MSW Processing Technologies.......................................... 4-2
Table 4-2 Alternative MSW Processing Technology Evaluation Matrix ......................... 4-3
Table 4-3 Characteristics of Black Bin Contents, City of Los Angeles, 2004.................. 4-8
Table 4-4 Technology Supplier Short List ........................................................................ 4-9
Table 5-1 Thermal Conversion Facilities.......................................................................... 5-7
Table 5-2 Advanced Thermal Conversion Facilities......................................................... 5-9
Table 5-3 Biological Conversion Facilities..................................................................... 5-10
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List of Figures Page
Figure 6-5 Advanced Thermal Recycling Process Diagram .............................................. 6-8
Figure 6-6 Pyrolysis/Gasification Scenario Illustration ..................................................... 6-9
Figure 6-7 Pyrolysis/Gasification Process Flow Diagram................................................ 6-10
Figure 6-8 Waste Conversion (Anaerobic Digestion) Scenario ....................................... 6-12
Figure 6-9 Anaerobic Digestion Process Flow Diagram.................................................. 6-12
Figure 6-10 Annual Net Energy Consumption by Scenario............................................... 6-15Figure 6-11 Annual Net Pounds of Criteria Air Emissions by Scenario............................ 6-17
Figure 6-12 Annual Net Metric Tons of Carbon Equivalent by Scenario.......................... 6-19
Figure 7-1 Alternative Technologies for Treating Black Bin
Post-Source Separated MSW............................................................................ 7-2
Figure 7-2 Throughput by Supplier (TPY)......................................................................... 7-4
Figure 7-3 Net Electricity Production, MW ....................................................................... 7-6Figure 7-4 Energy Efficiency, Net kWh/Ton ..................................................................... 7-6
Figure 7-5 Diversion Rate, Percent of Throughput ............................................................ 7-9
Figure 7-6 Capital Cost, $/TPY........................................................................................ 7-15
Figure 7-7 Total Revenue/Ton by Supplier ...................................................................... 7-16
Figure 7-8 Estimated Breakeven Tipping Fee and
Worst Case Breakeven Tipping Fee ............................................................... 7-18
Figure 7-9 Objectives Hierarchy ...................................................................................... 7-19Figure 7-10 Total Ranking Score by Supplier.................................................................... 7-26
List of Appendices
Appendix A Master Supply List of Technologies
Appendix B Characterization of Alternative Waste Processing Technologies
Appendix C Europe Facilities Field ReportsAppendix D Life Cycle Analysis Report
Appendix E Supplier Evaluations
Appendix F Alternative Technology RFQ
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LIST OF ACRONYMS AND ABBREVIATIONS
AB Assembly BillAC Alternating Current (Electric)
AD Anaerobic Digestion
ADC Alternative Daily Cover
AQMD Air Quality Management District
ATR Advanced Thermal Recycling
BACT Best Available Control Technology
BETF Break Even Tipping FeeBtu British Thermal Unit
CAP Compost Analysis Proficiency
CARB California Air Resources Board
CCQC California Compost Quality Council
CDFA California Department of Food and Agriculture
CEC California Energy Commission
CEQA California Environmental Quality ActCIWMB California Integrated Waste Management Board
CNG Compressed Natural Gas
CT Conversion Technology
DC Direct Current (Electric)
EPA Environmental Protection Agency
HCl Hydrochloric Acid
HHV Higher Heating ValveHRSG Heat Recovery Steam Generator
kW Kilowatt
kWh Kilowatt hour
lb Pound
LEA Local Enforcement Agencies
LHV Lower Heating Valve
MBtu Million British Thermal UnitsMRFs Material Recovery Facilities
MSW Municipal Solid Waste
MW Megawatt
MWe Megawatt Electric
MWh Megawatt hour
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LIST OF ACRONYMS AND ABBREVIATIONS
OGM Organic Growth MediumPFRP Processed to Further Reduce Pathogens
PM Particulate Matter
PUC Public Utilities Commission
QA Quality Assurance
QC Quality Control
RDF Refuse Derived Fuel
RFQ Request For QualificationsRPS Renewable Portfolio Standard
RSI Report of Site Information
RWQCB Regional Water Quality Control Board
SCAQMD South Coast Air Quality Management District
scf Standard Cubic Foot
SCR Selective catalytic reduction
SNCR Selective non-catalytic reductionSTA Seal of Testing Assurance
SWMP Solid Waste Management Plan
SWPPP Storm Water Pollution Prevention Plan
SWRCB State Water Resources Control Board
TCLP Toxicity Characteristic Leaching Procedure
TMECC Test Methods for the Examination of Composting and Compost
TPD Tons Per DayTPY Tons Per Year
USCC United States Composting Council
USEPA United Stated Environmental Protection Agency
VOC Volatile Organic Compound
WCTF Worst Case Tipping Fee
WDR Water Discharge Requirements
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EXECUTIVE SUMMARY
The City of Los Angeles Department of Public Works, Bureau of Sanitation engaged URSCorporation to conduct an evaluation of alternative municipal solid waste (MSW) processing
technologies to process residential refuse, or post-source separated MSW. The City uses
three bins to collect solid waste from residences: green bin (green waste), blue bin
(recyclables), and black bin (refuse). The green and blue bin material is recycled. The black
bin refuse, or post-source separated MSW, which is landfilled, is the subject of this study.
The study began with development of the Citys overall project objectives. The highest-level
objective is:
Identify alternative MSW processing technologies that will increase landfill
diversion in an environmentally sound manner, while emphasizing options
that are energy efficient, socially acceptable, and economical.
This objective was subdivided into three lower-level objectives:
Maximize Environmental (Siting) Feasibility (i.e., minimize impacts to the environmentand citizens)
Maximize Technical Feasibility (i.e., search for technologies that are commercially
available within the development timeframe of 2005-2010 and will significantly increase
diversion from landfills)
Maximize Economic Feasibility (i.e., provide an overall cost that is competitive with
other solid waste processing methods)
These objectives were applied, through the use of screening criteria, to identify potential
technologies that could meet the Citys objectives. Technologies initially identified were:
Thermal Technologies
Biological/Chemical Technologies
Physical Technologies
Thermal technologies are those technologies that operate at temperatures greater than 400
degrees F and have higher reaction rates. They typically operate in a temperature range of
700 degrees F to 10,000 degrees F. Most thermal technologies are used to produce electricity
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EXECUTIVE SUMMARY
processing carried out in multiple stages. Byproducts can vary, which include: electricity,compost and chemicals.
Physical technologies involve altering the physical characteristics of the MSW feedstock.
These materials in MSW may be separated, shredded, and/or dried in a processing facility.
The resulting material is referred to as refuse-derived fuel (RDF). It may be densified or
pelletized into homogeneous fuel pellets and transported and combusted as a supplementary
fuel in utility boilers.
All of these technologies are described in Section 2.0. The state and Federal regulations
governing the permitting of these technologies is presented in Section 3.0.
Twenty individual alternative MSW processing technologies were included within these
major categories. The technologies were screened using a set of basic technology capability
and experience criteria. Through this process, ten technologies within the technology groups
of thermal and biological technologies were identified that meet the applicable criteria (seeSection 4.3).
About 225 suppliers were screened, and twenty-six suppliers were selected to submit their
detailed qualifications to the City. These qualifications were to include information about the
suppliers experience, descriptions of several reference facilities, and a preliminary
description of a proposed facility for the City of Los Angeles (see Section 5.1).
Of the twenty-six suppliers requested to submit qualifications, seventeen provided responses.
These suppliers and their technologies were thoroughly evaluated (including several site
visits). This evaluation primarily was based upon the information and data contained in the
submittals received. These submittals ranged from very responsive to incomplete. Each
supplier was requested to provide additional information based on an initial review. Tables
5-1 through 5-3 provide a good summary of the information obtained from each supplier.
Additional detail is presented in Appendix E.
The supplier data contained in Section 5.0 and Appendix E were used to prepare a life cycle
analysis associated with implementation of alternative waste processing technologies in the
Citys integrated solid waste management system. This allows the City of Los Angeles to
more accurately compare these new technologies to existing solid waste management
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EXECUTIVE SUMMARY
Finally, the supplier data were used to conduct a comparative analysis of the technologies,and rank the suppliers to select technologies for further assessment. The comparative analysis
addressed a number of technical, environmental, and cost issues, including:
Throughput (respondents provided data for different throughput rates)
Electricity production
Net efficiency in kWh/ton feedstock
Diversion rate
Air emissions
Solid wastes
Regulatory issues
Capital cost Revenues
Estimated tipping fees
A supplier ranking process was employed to help select the most attractive technologies for
treating the Citys black bin post-source separated MSW. Evaluation criteria were defined,
performance levels established, and scores computed to develop a ranking of suppliers and
technologies.
The comparative analysis and ranking is presented in Section 7.0.
FINDINGS
The study evaluated the ability of alternative technologies to process black bin post-source
separated MSW from three perspectives: siting (or environmental) feasibility, technicalfeasibility, and economic feasibility. The results of this evaluation, in part, can be expressed
in terms of key findings that impact the overall study conclusions and recommendations that
follow.
Table ES-1 provides a summary of these key findings. The table is arranged by objective
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EXECUTIVE SUMMARY
Thermal technologies Advanced thermal recycling, and thermal conversion (includespyrolysis, gasification and pyrolysis-gasification)
Biological/chemical Anaerobic digestion
Physical None (Section 4.3)
As a result, the key findings address advanced thermal recycling, thermal conversion, and
biological conversion.
Table ES-1 includes references to report sections where each finding is discussed in more
detail.
CONCLUSIONS
Based upon the key findings from Section 8.1 and the technology ranking presented in
Section 7.4, the following conclusions are made:
An alternative MSW processing facility can be successfully developed in the City of Los
Angeles.
The technologies best suited for processing black bin post-source separated MSW on a
commercial level are the thermal technologies. These include advanced thermal recycling
and thermal conversion (pyrolysis and gasification).
The biological/chemical conversion technologies and physical technologies present
significant technical challenges for treatment of the black bin post-source separated
MSW. While biological conversion technologies show the most promise in this group,
they also bring significant challenges, as explained below.
The technology ranking in Section 7.4 evaluated the thermal and biological technologies
using eight criteria that addressed siting, technical, and economic issues. While the ranking
was conducted using supplier data, the results were used to decide which technology groupsexhibited the best characteristics with regard to successfully processing of black bin post-
source separated MSW.
Based upon the ranking scores in terms of technologies rather than suppliers, the following
l i d
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EXECUTIVE SUMMARY
Initiate Public Outreach
Public acceptability will be one of the most important determinants of this projects success.
Siting, permitting and developing a new alternative MSW processing technology for the City
of Los Angeles will lead to many questions from the public with regard to environmental
impacts and public health issues. The key is to consider the public as a partner and present
the facts and benefits as early as possible while being responsive to their concerns at all
times. Developing early relationships with key stakeholder groups is essential.
The public outreach should be conducted in two phases. The first phase begins in 2005, with
two purposes: educate the public about the alternative MSW processing technologies, and
elicit feedback regarding the publics attitude toward the technologies under consideration.
Education about the characteristics of the technologies, compared to existing disposal
methods, their benefits, and their anticipated environmental impacts are critical tasks. Public
outreach is also important at this stage to provide counterpoint to opposing groups. A
communications strategy in the first phase will access the public in broad terms, to reachlarge audiences, using techniques such as television spots, radio interviews, press
conferences, and editorial pieces. Selected focus groups, as well as meetings with community
leaders, agency personnel knowledgeable about emerging MSW processing technologies,
and environmental groups also would be helpful.
The second phase of public outreach takes place after the technology supplier is selected and
alternative site locations are known. Then the outreach becomes more specific than before,and is focused on the communities, which could be directly affected by the project. The
communications strategy in this phase will use techniques that involve the affected
communities, such as Citizens Advisory Committees and specific neighborhood councils.
Develop a Short List of Suppliers
Prior to issuing a Request for Proposal (RFP) to select a supplier for the alternative MSW
processing technology, a list of suppliers eligible for receiving this RFP will be developed.
This short list will be compiled using the following input:
Results of the supplier evaluation conducted during this study
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EXECUTIVE SUMMARY
Conduct Initial Siting Study
An RFP must be quite specific with regard to site characteristics in order to encourage the
most detailed and complete responses. Potential bidders will want to know more information
about site environmental constraints and availability of infrastructure. This information must
be compiled while the RFP is being prepared.
Prepare a Request for Proposal and Select Preferred Suppliers
A technology supplier must formally be selected for this project. This will be accomplished
by issuing an RFP to selected bidders. The RFP will contain a detailed set of instructions
about how to reply, and will require the bidder to provide a comprehensive design along with
a detailed cost and revenue estimate and information on performance guarantees and
financing. The responses to the RFP will be evaluated, and a preferred supplier will be
selected.
Conduct Facility Permitting and Conceptual Design
Once a technology supplier has been selected, a conceptual design is prepared to support
preparation of required environmental and permit application documents. In parallel, these
environmental documents will be prepared, and submitted to the appropriate agencies for
processing. A series of public meetings will be held during agency review.
Perform Detailed Design and Construction
Finally, the detailed design is prepared, which will support facility construction, followed by
construction, start-up, and initiation of operation. Commercial operation is targeted for 2010.
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SECTION 1.0 IDENTIFY ALTERNATIVE MSW PROCESSING TECHNOLOGIES
1.1 INTRODUCTION
The City of Los Angeles Department of Public Works, Bureau of Sanitation (hereinafter
referred to as the Bureau) engaged URS Corporation to undertake a study of alternative
Municipal Solid Waste (MSW) processing technologies to process residential refuse, or post-
source separated MSW. The City uses three bins to collect solid waste from residences:
green bin (green waste), blue bin (recyclables), and black bin (refuse). The green and blue
bin material is recycled. The black bin refuse, or post-source separated MSW, which is
landfilled, is the subject of this study.
This report, which provides the results of this study, is organized as follows:
Section 1.0 Identify Alternative MSW Processing Technologies
Section 2.0 Characterize Alternative MSW Processing Technologies
Section 3.0 Regulations Affecting MSW Processing Technology Implementation
Section 4.0 Screening Alternative MSW Processing Technologies
Section 5.0 Detailed Assessment of Alternative MSW Processing Technologies and
Suppliers
Section 6.0 Life Cycle Analysis
Section 7.0 Comparative Analysis of Alternative MSW Processing Technologies and
Suppliers
Section 8.0 Conclusions and Recommendations
The first step in the study was to identify a set of technologies that potentially could process
black bin post-source separated MSW generated by the City of Los Angeles. These
technologies are characterized in Section 2.0. The regulatory environment for permitting
alternative waste processing technologies is presented in Section 3.0. Then the technologieswere screened and potential suppliers identified in Section 4.0. Suppliers were brought into
this study to allow more detailed evaluation of technology designs, environmental impacts,
and economics. Note that the study concludes by identifying suitable technologies.
A Request for Qualifications was sent to the potential suppliers and the evaluation of
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SECTION 1.0 IDENTIFY ALTERNATIVE MSW PROCESSING TECHNOLOGIES
1.2 BUSINESS OBJECTIVES
The Bureaus overall objective is to identify alternative MSW waste processing
technologies that will increase landfill diversion in an environmentally sound manner, while
emphasizing options that are energy efficient, socially acceptable, and economical. All of
the evaluation criteria used in this study were derived in part from the project objectives.
These criteria were used to select, screen, and rank the technologies and suppliers.
1.3 EVALUATION METHODOLOGY
The method selected to identify screening and ranking criteria is termed top-down, and
starts with defining the Bureaus project objectives that must be satisfied. These broad
objectives are subdivided to define lower-level objectives. Each level of subdivision results
in further definition. This process ceases when the lowest level entries, or criteria, are
defined.
Criteria, in order to be effective, must be complete, so that all issues are considered;
measurable, so that the criteria can be used in the analysis; and non-redundant, so that
double counting of issues is avoided.
One way to conduct the top-down process to define criteria is to use a device called an
objectives hierarchy. This diagram displays the top-level and lower-level project
objectives, and, if drawn to completion, the criteria. Figure 1-1 shows the business objectives
hierarchy developed for this task.
The top-level objective, as mentioned above, is identify alternative MSW waste processing
technologies that will increase landfill diversion in an environmentally sound manner, while
emphasizing options that are energy efficient, socially acceptable, and economical or, in
short, Identify a Suitable Alternative MSW Processing Technology. This is the overarching
objective.
The second level in the figure shows three sub-objectives: Maximize Siting Feasibility;
Maximize Economic Feasibility; and Maximize Technical Feasibility. If these objectives are
satisfied, the overarching objective will be satisfied. The Bureau specified siting, economics,
and technical issues as key project objectives for deciding upon acceptable technologies for
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SECTION 1.0 IDENTIFY ALTERNATIVE MSW PROCESSING TECHNOLOGIES
The Maximize Economic Feasibility objective is broken down to minimizing cost andmaximizing revenues, and the ability to generate marketable byproducts.
The Maximize Technical Feasibility is separated into Minimize Development Risk and
Minimize Landfill Residuals. These sub-objectives are further divided into maximizing the
use of commercial and late-emerging technologies, maximizing the treatment efficiency of
black bin post-source separated MSW, and the ability to process at least 200 tons per day
(TPD) of feed at a rate approximately equal to one-third (1/3) of one of the six Los Angeles
waste sheds.
At this point, six sub-objectives have been identified, as shown at the lowest level in Figure
1-1. These definitions are still too general for use as screening or ranking criteria. However,
they can be helpful for defining suitable technologies and, subsequently, technology
suppliers.
FIGURE 1-1BUSINESS OBJECTIVES
CITY OF LOS ANGELES ALTERNATIVE MSW PROCESSING STUDY
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SECTION 1.0 IDENTIFY ALTERNATIVE MSW PROCESSING TECHNOLOGIES
1.4 ALTERNATIVE MSW PROCESSING TECHNOLOGIES
For purposes of this study, alternative waste processing technologies can be separated into
three groups or categories:
Thermal Technologies
Biological/Chemical Technologies
Physical Technologies
Thermal technologies operate at temperatures greater than 400F and have higher reaction
rates. They typically operate in a temperature range of 700F to 10,000F. Most thermal
technologies are used to produce electricity as a primary byproduct. Thermal technologies
include advanced thermal recycling and thermal conversion.
Biological/chemical technologiesoperate at lower temperatures and lower reaction rates.They can accept feedstock with high moisture levels, but require material that is
biodegradable. Some technologies involve the synthesis of products using physical chemistry
and chemical processing carried out in multiple stages. Byproducts can vary, which include:
electricity, compost, and chemicals.
Physical technologies involve altering the physical characteristics of the organic portion of
the MSW feedstock. These materials in MSW may be separated, shredded, and/or dried in a
processing facility. The resulting material is referred to as refuse-derived fuel (RDF). It may
be densified or pelletized into homogeneous fuel pellets and transported and combusted as a
supplementary fuel in utility boilers.
Table 1-1 shows the technologies expressed in terms of the three major groups (thermal,
biological/chemical, and physical). These technology groups are then subdivided, into about
twenty technologies.
1.5 LIST OF TECHNOLOGY SUPPLIERS
A list of suppliers was compiled of the alternative waste processing technologies listed in
Table 1-1. This list is reproduced as Tables A-1 through A-4 in Appendix A. The table has
three sections corresponding to the three waste processing technology groups The criteria for
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SECTION 1.0 IDENTIFY ALTERNATIVE MSW PROCESSING TECHNOLOGIES
TABLE 1-1CLASSIFICATION OF MSW PROCESSING TECHNOLOGIES
Technology Group Technology
Advanced Thermal Recycling
Pyrolysis
Pyrolysis/Gasification
Pyrolysis/Steam Reforming
Conventional Gasification Fluid Bed
Conventional Gasification Fixed Bed
Thermal Technologies
Plasma Arc Gasification
Anaerobic Digestion
Aerobic Digestion/Composting
Ethanol Fermentation
Syngas-Ethanol
BiodieselThermal Depolymerization
Biological/Chemical
Catalytic Cracking
Refuse Derived Fuel (RDF)
Densification/Pelletization
Drying
Mechanical Separation
Size Reduction
Physical
Steam Processing/Autoclaving
This list was developed from a number of sources, including the following:
California Integrated Waste Management Board (CIWMB) list included in their report on
conversion technologies
Santa Barbara County list
Riverside County list
City of Alameda list
City of Honolulu list
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SECTION 1.0 IDENTIFY ALTERNATIVE MSW PROCESSING TECHNOLOGIES
Southern California Association of Governments list City of Los Angeles list
In addition, a web search was performed of alternative MSW processing technologies,
concentrating on thermal, biological/chemical, and physical technologies. These results were
added to the list.
Descriptions of the technologies are provided in Section 2.0.
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CHARACTERIZE ALTERNATIVE
SECTION 2.0 MSW PROCESSING TECHNOLOGIES
2.1 INTRODUCTION
The alternative MSW processing technologies identified in Section 1.0 are characterized in
terms of their process description, throughput, feedstock composition, byproducts generated,
and environmental issues. This description is general and only key technology groups are
addressed.
These technologies represent the vast majority of the alternative solid waste processingtechnology suppliers. The technologies addressed in this section are:
Thermal
Advanced Thermal Recycling
Pyrolysis
Pyrolysis/Gasification
Pyrolysis/Steam Reforming
Conventional Gasification Fluid Bed
Conventional Gasification Fixed Bed
Plasma Arc Gasification
Biological/Chemical
Anaerobic Digestion
Aerobic Digestion/Composting
Ethanol Fermentation
Syngas-Ethanol
Biodiesel
Thermal Depolymerization
Catalytic Cracking
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CHARACTERIZE ALTERNATIVE
SECTION 2.0 MSW PROCESSING TECHNOLOGIES
Size Reduction
Steam Processing/Autoclaving
The solid waste processing technologies evaluated in this study include advanced thermal
recycling and a group of technologies commonly referred to as conversion facilities.
Advanced thermal recycling is a second-generation advancement of technology that utilizes
complete combustion of organic, carbon-based materials in an oxygen-rich environment, as
described in Section 2.2.
A conversion facility typically consists of the four components shown in the rectangles of
Figure 2-1.
FIGURE 2-1
ANATOMY OF A CONVERSION FACILITY
ProductionConversionPre-
Processing
PostConversionClean-up &Processing
MSWInput
ByproductsRecyclables
AirEmissions
Solid/LiquidResiduals
Solid/LiquidResiduals
Electricity/Chemicals
The first component involves pre-processing of the feedstock. The purpose of the pre-
i i f ld i i l bl i l ( l l)
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The second component is the conversion unit. This unit will process the prepared feedstock
and generate certain byproducts, which can usually be marketed. In addition, the conversion
unit may produce a small quantity of solid or liquid residuals that could be disposed in a
landfill.
Some conversion units will produce an output that requires another processing step before
use. For example, if a synthetic fuel gas or biogas is generated, the gas will undergo cleaning
and further processing before being used to produce energy in the fourth component. A smallquantity of solid or liquid residuals may be created in this step as well. Other conversion
systems move from the conversion step directly to the production step.
The final output from the conversion unit is used in a production process. In many cases, a
synthetic gas or biogas is input to a power facility that produces electricity for sale into the
power grid. This production unit does produce air emissions and sometimes a small quantity
of solid residual.
Each of these components is described in more detail in the following sections.
2.2 THERMAL PROCESSING TECHNOLOGIES
The thermal processing technologies being considered for this evaluation are technologies
that thermally process MSW.
These technologies include:
Advanced thermal recycling
Pyrolysis
Pyrolysis/gasification
Pyrolysis/steam reforming
Conventional gasification (fixed bed and fluid bed)
Plasma arc gasification
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waste gases flow through an advanced emission control system designed to capture and
recover components in the flue gas, converting them to marketable by-products such as
gypsum (e.g., for wallboard manufacture) and hydrochloric acid (used for water treatment).
The bottom ash and fly ash are segregated, allowing for recovery/recycling of metals from
the bottom ash, and use of the bottom ash as a road base and construction material. The
advanced recycling and emission control systems with recovery/recycling go beyond the
technology utilized at conventional resource recovery plants such as the Commerce Refuse-
to-Energy facility and the Southeast Resource Recovery facility.
Pyrolysis The thermal degradation of organic carbon-based materials through the use of an
indirect, external source of heat, typically at temperatures of 750F to 1,650F, in the
absence or almost complete absence of free oxygen. This thermally decomposes and drives
off the volatile portions of the organic materials, resulting in a syngas composed primarily of
hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), and methane (CH4). Some of
the volatile components form tar and oil, which can be removed and reused as a fuel. Mostpyrolysis systems are closed systems and there are no waste gases or air emission sources (if
the syngas is combusted to produce electricity, the power system will have air emissions
through a stack and air emission control system). After cooling and cleaning in emission
control systems, the syngas can be utilized in boilers, gas turbines, or internal combustion
engines to generate electricity or used to make chemicals. The balance of the organic
materials that are not volatile, or liquid that is left as a char material, can be further processed
or used for its adsorption properties (activated carbon). Inorganic materials form a bottomash that requires disposal, although some pyrolysis ash can be used for manufacturing brick
materials.
Gasification The thermal conversion of organic carbon-based materials in the presence of
internally produced heat, typically at temperatures of 1,400F to 2,500F, and in a limited
supply of air/oxygen (less than stoichiometric, or less than is needed for complete
combustion) to produce a syngas composed primarily of H2 and CO. Inorganic materials areconverted either to bottom ash (low-temperature gasification) or to a solid, vitreous slag
(high temperature gasification that operates above the melting temperature of inorganic
components). Some of the oxygen injected into the system is used in reactions that produce
heat, so that pyrolysis (endothermic) gasification reactions can initiate; after which, the
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2.2.1.3 Feedstock Characteristics
The feedstock for advanced thermal recycling systems can be unprocessed MSW or RDF.
Using lower moisture content, RDF improves the heating value of the feedstock, resulting in
higher efficiency and lower throughput per kilowatt-hour (kWh) of electricity generated.Inorder to improve economics and efficiency, facilities can incorporate pre-processing to
remove marketable recyclables, such as paper, plastics, metals, and glass. Pre-processing of
black bin contents (recyclables already being removed) may not yield the benefits seen withmixed MSW.
2.2.1.4 Solid Byproducts
In order to improve the operating performance and efficiency, significant effort is made to
recover recyclables in the pre-processing step, as well as recovering, processing, cleaning,
and recycling bottom ash and slag. Most advanced thermal recycling systems produce apowdery to granular bottom ash. If the grate/furnace system is designed to produce a sintered
ash, it may be more like slag, which is glassy and non-hazardous, and may be able to be used
for making construction materials. Since some hydrochloric acid (HCl) is formed during
combustion (from combustion of chlorine-containing plastics and salt), this can be removed,
cleaned, concentrated, and sold. Sulfur compounds in the MSW are converted to sulfur
dioxide (SO2), which can be separately removed with a lime or limestone scrubber, where the
sulfur dioxide is converted to calcium sulfate (CaSO4), or gypsum. Chemically produced
gypsum is currently sold around the world for use in manufacturing wallboard and cement.
Depending on the local market, the gypsum may be saleable.
2.2.1.5 Environmental Issues
Air emissions are likely to be a key environmental issue for advanced thermal recycling
facilities. In thermal recycling, combustion of MSW is achieved in the presence of a direct
flame and an over-abundance of combustion air to promote the complete oxidation of theincoming waste to form primarily carbon dioxide and water vapor that are emitted along with
the excess combustion air (the portion of the incoming air that is not required for oxidation).
The combustion process can be expected to cause emissions of gas-phase air pollutants and
particulate matter (for which California and National ambient air quality standards have been
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Automated combustion controls and furnace geometry designed to optimize residence
time, temperature, and turbulence to ensure complete combustion.
Selective non-catalytic reduction (SNCR) system in the boiler for reduction of oxides of
nitrogen (NOx) emissions. Selective catalytic reduction (SCR), which is more efficient
than SNCR, would be evaluated for potential feasibility.
Baghouse (fabric filter) with activated carbon injection for removal of trace metals and
trace organics concentrated on the particulate matter.
Scrubber for chlorides/HCl (may produce saleable HCl a commonly used commercial
and laboratory chemical).
Scrubber for SO2 (may produce saleable gypsum a material routinely used in the
cement industry).
Secondary activated carbon for trace organic and metals.
Final baghouse for removal of fine particulate after scrubbers.
All of these emission control systems are well-demonstrated technologies that would be able
to control emissions to levels well below regulatory limits in California.
In addition to air emissions, the key environmental issues relating to constructing and
operating an advanced thermal recycling facility include:
Traffic Facilities must be sized to be economic, which likely will require 100+ trucks
per day to deliver feedstock. Thus, traffic impacts may be significant.
Ash Disposal Advanced thermal recycling systems create about 30% residuals. About
5% of this material will be disposed in a landfill.
Aesthetics and View Corridor These facilities have relatively tall stacks, which may
create visual impacts due to the structure, or plume visibility issues under certainoperating and weather conditions.
To a lesser degree, there will be concerns about noise, dust, and odors.
2 2 2 Pyrolysis
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FIGURE 2-3
TYPICAL PYROLYSIS SYSTEM FOR POWER GENERATION OR CHEMICALS
2.2.2.1.1 Conventional Pyrolysis. Pyrolysis has a long history of industrial use. Pyrolysis
systems utilize a wide range of designs, temperatures, and pressures to initiate pyrolysis
reactions. Typically, pyrolysis systems use a drum, kiln-shaped structure, or pyrolysis tube,
which is externally heated using either recycled syngas or another fuel or heat source, to heat
the pyrolysis tube/chamber. Basically, the organic materials are cooked in an oven with no
air or oxygen present. No burning takes place.
Most organic compounds are thermally unstable. At high temperatures, the organiccompounds volatilize and bonds thermally crack, breaking larger molecules into gases and
liquids composed of smaller molecules, including hydrocarbon gases and hydrogen gas. The
temperature, pressure, reaction rates, and internal heat transfer rates are used to control
specific pyrolytic reactions in order to produce specific products. At lower temperatures,
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CH3 + H CH4
Pyrolysis reactions are endothermic, meaning they require externally supplied heat to occur.
Natural gas, propane, or syngas produced by pyrolysis can be used as a source of external
heat. If the feedstock has a large higher heating value (HHV) measured in Btu/lb, the
pyrolytic process becomes more self-sufficient, and once the process starts, it uses an
extremely small amount of fossil fuel. Also, some partial oxidation (from trapped air as well
as oxygen in the organic compounds, especially when biomass is used) of the methane gasoccurs to form CO, with some CO2 formed as the carbon reacts:
2CH4 + O2 2CO + 4H2
CH4 + 1O2 CO + 2H2O
C + O2 CO
C + O2 CO2
These reactions are exothermic (producing heat), helping to maintain the internal
temperatures required for pyrolysis. Another reaction that occurs is reformation, where the
products of the reactions noted above begin to combine with each other, forming other
reaction byproducts. Two of the common reactions are: 1) where carbon reacts with water to
form carbon monoxide and hydrogen, the main components of syngas,
C + H2O CO + H2 (water-gas reaction)
and 2) where carbon reacts with carbon dioxide to form two molecules of carbon monoxide:
C + CO2 2CO (Boudouard reaction)
These reactions are key to pyrolysis. They produce the constituents of syngas, CO and H 2,which are combustible gases. They also consume oxidized compounds (CO2 and H2O),
which have no heating value in syngas and dilute it. The reactions are endothermic, using the
heat produced in the exothermic reactions noted above, helping to maintain and control the
overall reactor temperature.
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Since inorganic materials do not enter the thermal conversion reactions, energy, which could
be used to produce pyrolysis reactions, is expended in heating up the inorganic materials to
the pyrolysis reactor temperature. The inorganic materials are cooled in cleanup processes,
and heat is lost. Pre-processing is required to remove inorganic materials such as grit, glass,
and metal, and to enhance the homogeneity of the feedstock. Depending on the specific
pyrolysis process, pre-processing may include several of the physical processes described in
Section 2.3.
Since pyrolysis occurs in the absence of oxygen, the feed system and pyrolysis chamber are
sealed and isolated from outside air during the processing. This is accomplished through the
use of inlet and outlet knife-gates, with ram feeders to feed individual plugs of feedstock
into the reactor as the next plug is being fed into the sealed environment.
In the reactor, pyrolysis may occur over a period of time (as much as an hour in a pyrolysis
or degassing chamber) or very quickly, as in the case of flash pyrolysis, where thefeedstock encounters an extremely hot internal surface and volatilizes in less than a second.
Slow pyrolysis is used to maximize the production of char, as in the case of producing
charcoal or activated carbon. In those cases, the volatile fraction may be vented or used
elsewhere. Slow pyrolysis is used to convert low volatile coal to metallurgical grade coke for
steel making. Coke is a very pure carbon product, which is then used to initiate a reducing
atmosphere for converting iron ore to molten iron.
Following the pyrolysis reactor, the syngas may be:
Burned directly in a thermal oxidizer or boiler, and its heat recovered for making steam
for power generation. The exhaust gases then pass through emission control systems that
may include fabric filters, wet and dry scrubbers, electrostatic precipitators, and/or
activated carbon beds.
Quench cooled, cleaned in emission control systems, and then burned in a boiler,
reciprocating engine, or gas turbine for power generation.
Quench cooled, cleaned in emission control systems, and then utilized for producing
organic chemicals.
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2.2.2.1.2 Pyrolysis/Steam Reforming. Figure 2-4 presents a typical process description for
a pyrolysis/steam reforming facility.
FIGURE 2-4
TYPICAL PYROLYSIS/STEAM REFORMING SYSTEM
FOR POWER GENERATION
Since the pyrolysis reactions result in the formation of char, liquids, and/or gases, additional
reactions can be initiated to further the thermal breakdown of these organic compounds. One
of the common reactions to follow pyrolysis is steam reforming. As noted below, the water-gas reaction is used to promote the reaction of carbon and water to form syngas. In this
manner, the char produced in pyrolysis is reacted with steam that is injected into the process
so that:
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The syngas stream is then cooled, cleaned, and used for power generation or chemical
production.
2.2.2.2 Throughput
Existing pyrolysis systems treat up to 300 tpd with pyrolysis/steam reforming systems
operating at 165 tpd. Systems are modular and can be installed in parallel to increase
throughput.
2.2.2.3 Feedstock Characteristics
Pyrolysis systems can process a wide range of carbon-based materials. Any organic or
thermally degradable material can be processed by pyrolysis. Historically, pyrolysis was used
to make charcoal from wood. Pyrolysis also is used to process used tires and produce carbon
black, steel, and fuel to generate power. Currently, some manufacturers are using pyrolysis to
make activated carbon using coconut shells or wood as feedstock. If a homogeneous
feedstock is processed by pyrolysis, a high quality byproduct is produced.
MSW is not a homogenous waste stream. In order to make the pyrolysis process more
efficient, pre-processing of MSW is required. The pre-processing includes the separation of
thermally non-degradable material such as metal, glass, and concrete debris. Also, for some
pyrolytic processes, size reduction and/or densification of the feedstock may be required. If
MSW has a high moisture content, a dryer may be added to the pre-processing stage to lowerthe moisture content of the MSW to 25% or lower, because lower moisture content of the
feedstock increases its heating value and the system becomes more efficient. The waste heat
or fuel produced by the system can be used to dry the MSW.
2.2.2.4 Solid Byproducts
The solid byproducts from pyrolysis are mainly carbon char, silica, metal, and non-thermally
degradable material such as glass. In the case of low temperature pyrolysis, where liquid fuel
is the byproduct, a tar or viscous material is also produced. The carbon char from processing
MSW can be used as fuel, additives to construction materials, or for other industrial
purposes. The carbon char produced by pyrolysis can be activated using the steam generated
b h l i Th i d b b d i f ili i
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thermal conversion technologies, they may have inherently lower air emissions and thus offer
environmental benefits when compared to advanced thermal recycling facilities. These
design and operation characteristics include:
Since pyrolysis and gasification processes occur in a reducing environment, typically
using indirect heat, and without free air or oxygen, or with a limited amount of air or
oxygen, the formation of unwanted organic compounds or trace constituents is
minimized.
Pyrolysis and gasification reactors are typically closed, pressurized systems, so that there
are no direct air emission points. Contaminants are removed from the syngas and/or from
the flue gases prior to being exhausted from a stack.
Thermal conversion technologies often incorporate pre-processing subsystems in order to
produce a more homogeneous feedstock; this provides the opportunity to remove
chlorine-containing plastics (as recyclables), which could otherwise contribute to theformation of organic compounds or trace constituents.
The volume of syngas produced in the conversion of the feedstock is considerably lower
than the volume of flue gases formed in the combustion of MSW in advanced thermal
recycling facilities. Smaller gas volumes are easier and less costly to treat, and allow for
the use of a wider variety of control technologies.
Pre-cleaning of the syngas is possible prior to combustion in a boiler, and is requiredwhen producing chemicals or prior to combustion in a reciprocating engine or gas turbine
in order to reduce the potential for corrosion in this sensitive equipment. Syngas pre-
cleaning serves to reduce overall air emissions.
Syngas produced by thermal conversion technologies is much more homogeneous and
cleaner-burning fuel than MSW.
Air emission control and processing systems that are likely to be required by South Coast AirQuality Management District (SCAQMD) include some or all of the following:
When the syngas is combusted in a boiler, reciprocating engine, or gas turbine, automated
combustion controls and furnace geometry (for boilers) designed to optimize residence
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Activated carbon injection (followed by a baghouse) for removal of trace metals (such as
mercury).
Wet scrubber for removal of chlorides/HCl (may produce saleable HCl).
Wet, dry, or semi-dry scrubber for SO2 (may produce saleable gypsum).
Final baghouse for removal of fine particulate matter after dry or semi-dry scrubbers.
Air emission control equipment to accomplish this syngas and/or flue gas cleanup is
commercially available, and is able to reduce air emissions to levels well below regulatory
limits in California.
In addition to air emissions, the key environmental issues relating to constructing and
operating a pyrolysis facility include:
Traffic If the facility is not located at an existing waste management facility (e.g.,transfer station), some traffic impacts will occur due to delivery of feedstock.
Solid residue management Inorganic constituents may be produced as bottom ash or
slag, depending on the temperature in the reactor. Bottom ash, if not sold, can be
disposed in a landfill. Slag, which is glassy and non-hazardous, is typically sold for the
uses noted above. If markets are not available, it can be safely landfilled.
Visual and Land Use There may be impacts relating to the visual character of thefacility or issues relating to compatibility of the facility with surrounding land uses.
As with other facilities handling MSW, there will be concerns about odors, litter, noise,
and dust.
2.2.3 Gasification
2.2.3.1 Process Description
Figure 2-5 presents a process description for a typical gasification system. Individual process
components are discussed below.
2 2 3 1 1 Conventional Gasification Conventional gasification involves the partial
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FIGURE 2-5
TYPICAL GASIFICATION SYSTEM FOR
POWER GENERATION (2 OPTIONS) OR CHEMICALS
The Fischer-Tropsch process was developed to take syngas from gasification of coal and
convert it to a wide range of hydrocarbon liquids, including diesel. After WWII, the use of
gasification declined as oil and gasoline became cheaper and more available.
The use of gasification for MSW began in the 1980s in Europe and Japan. In these initial
units, the use of unprocessed MSW resulted in many technical problems, primarily due to the
heterogeneous nature of MSW. This caused handling and feeding problems, as well as issueswith temperature and process control, ash removal, and overall cost. Many of these facilities
were shut down. With the worldwide success in coal and petroleum coke gasification, and
regulatory requirements in Europe and Japan for increased diversion of MSW from landfills,
gasification became an alternative treatment technology for MSW. Most of the development
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by shredding and sorting. Others may require a significant amount of removal of recyclables,sorting, shredding, and drying, in order to provide a more homogeneous feedstock.
In the gasifier, the addition of air or oxygen for gasification of the MSW leads to a small
amount of combustion, forming some CO2 and releasing heat, which is used in progressing
the pyrolytic reactions:
C + O2
CO2
A significant amount of the heating value of the feedstock is used in this reaction. Utilizing
heat, the organic compounds in the feedstock begin to thermally degrade, forming the
pyrolysis gases, oils, liquids and char. As these products move through the bed or
downstream through the gasifier, they encounter air, oxygen, and/or steam, which are
injected to further the gasification reactions. Endothermic water-gas and Boudouard reactions
occur:
C + H2O CO + H2 (water-gas reaction)
Some of the carbon may react with the hydrogen, forming additional methane gas.
C + 2H2 CH4 (methanation reaction)
C + CO2 2CO (Boudouard reaction)
The Boudouard reaction is important in converting the CO2 from the partial combustion,
which has no heating value and dilutes the syngas, into CO, which is a primary component of
the syngas.
If air is used instead of oxygen, the syngas will include the nitrogen gas that enters with the
air, diluting the syngas and lowering its overall heating value. Gasifier designs are optimized
to feedstock and to specific reaction products. Additional water or steam can be injected toinitiate the water-gas shift reaction, which converts the CO formed in the water-gas and
Boudouard reactions to CO2, and then results in the production of a syngas stream higher in
hydrogen concentration:
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In fixed-bed gasifiers, the feedstock is usually fed through the system on a stationary ormoving grate. The air or oxygen is injected either up, down, or in a cross flow. In an updraft
gasifier, the air or oxygen is injected from the bottom and the syngas exits at the top. In a
downdraft design, the air enters at or near the top of the gasifier, and the syngas exits the side
or bottom.
In a fluid bed design, the gasifier is filled with inert particles (usually sand or alumina). The
feedstock is fed either directly into or above the bed. A high velocity gas, usually oxygen orair, is injected below the bed, causing the feedstock and inert particles to be suspended in the
bed. The feedstock and bed materials are continuously stirred, resulting in uniform
temperatures and reactions, and improved heat transfer. Bubbling bed and circulating fluid
bed designs are commonly used to enhance fluidization and turbulence.
Entrained flow gasifiers use large quantities of oxygen injected from the top or side of the
reaction chamber to create higher operating temperatures. This process is capable ofproducing a cleaner, tar-free syngas while keeping the gasified byproducts in a molten state,
allowing for easier disposal. This slag is both inert and virtually carbon free.
Following the gasifier, the syngas may be:
Burned directly in a thermal oxidizer or boiler, and its heat recovered for making steam
for power generation. The exhaust gases then pass through emission control systems that
may include fabric filters, wet and dry scrubbers, electrostatic precipitators, and/oractivated carbon beds.
Quench cooled, cleaned in emission control systems, and then burned in a boiler
reciprocating engine or gas turbine for power generation.
Quench cooled, cleaned in emission control systems, and then utilized for producing
organic chemicals.
If low temperature gasification is used, the inorganic materials in the feedstock will be
recovered as a powdery to clinker-like bottom ash. This can be disposed of or used for the
manufacture of block materials. If high-temperature gasification is used (typically above
about 2,000F), the inorganic materials will be subjected to temperatures above their melting
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pyrolysis or degassing chamber is pushed into the gasification chamber where the char andany pyrolysis liquids are gasified. While the pyrolysis reactor operates without free oxygen,
the gasification reactor may use air, oxygen, and/or steam to provide the oxygen needed for
gasification reactions. Gasification reactions are mostly exothermic, so that once the
reactions initiate, the process is self-sustaining.
Figure 2-6 presents a typical process description for a pyrolysis/gasification system.
FIGURE 2-6
TYPICAL PYROLYSIS/GASIFICATION SYSTEM FOR POWER GENERATION
2.2.3.2 Throughput
Existing gasification systems operate at throughputs up to 1,000 tpd, with pyrolysis/
gasification systems operating at 800 tpd. Gasifiers and the pre-processing, emission control,
and power generation systems can be installed in parallel to increase throughput and power
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designed for a homogeneous feedstock, although they can tolerate some variability. This canbe an issue with gasifiers that use a slurry feed, since significant changes in the feedstock
result in different slurry characteristics, potentially leading to inefficient gasification and
poor carbon conversion. When changes in the feedstock are anticipated, bench-scale or short-
term testing can be used to optimize gasifier operation.
Due to the heterogeneous nature of MSW, significant pre-processing is often required. While
some systems state that they can operate with little or no pre-processing, most includemanual picking for large appliances, followed by primary and secondary rotary/stationary
trommel screens, primary and secondary shredders, air classifiers, and magnetic and eddy-
current separators to remove glass and metals and reduce the feedstock size. Sizing/shredding
varies, with feedstocks ranging from 2 to 12 inches. Many systems incorporate an auger or
ram feeder that compacts the processed MSW feed to as little as 1/10th
of the original
volume. In order to increase efficiency, some systems incorporate drying to 10-20% moisture
content, using steam or engine exhaust. Depending on the supplier, as much as 2/3 of rawMSW may be removed prior to being fed into the gasifier.
2.2.3.4 Solid Byproducts
In low temperature gasification (below the melting point of most inorganic constituents), a
powdery to clinker-type of bottom ash is formed. In high temperature gasification, the
inorganic ash materials exit the bottom of the gasifier in a molten state, where the slag falls
into a water bath, and is cooled and crystallized into a glassy, non-hazardous slag. The slag is
crushed to form grit that can be easily handled. Slag can be used in the manufacture of
roofing tiles, sandblasting grit, and as asphalt filler. Bottom ash may require landfilling,
although some suppliers have been able to manufacture ceramic-like bricks or paving stones.
One system that utilizes oxygen injection creates extremely hot temperatures in the bottom of
the gasifier, reaching the melting temperature of some metals. In that process, metals can be
recovered in ingot form.
2.2.3.5 Environmental Issues
With regard to air emissions, the most important environmental issue for gasification, the
discussion in Section 2.2.2.5 applies here as well.
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sold, can be disposed in a landfill. Slag, which is glassy and non-hazardous, is typicallysold for the uses noted above. If markets are not available, it can be safely landfilled.
Visual and Land Use There may be impacts relating to the visual character of the
facility or issues relating to compatibility of the facility with surrounding land uses.
As with other facilities handling MSW, there will be concerns about odors, litter, noise,
and dust.
2.2.4 Plasma Arc Gasification
2.2.4.1 Process Description
Figure 2-7 presents a typical process description for a plasma arc gasification system.
FIGURE 2-7
TYPICAL PLASMA GASIFICATION SYSTEM FOR POWER GENERATION
Plasma is a hot ionized gas resulting from an electrical discharge Plasma technology uses an
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occurred for using plasma technology integrated with gasification technologies to processMSW. This has great potential to convert MSW to electricity more efficiently than
conventional pyrolysis and gasification systems, due to its high heat flux, high temperature,
almost complete conversion of carbon-based materials to syngas, and conversion of inorganic
materials to a glassy, non-hazardous slag.
There are two types of plasma torches, the transferred torch and the non-transferred torch.
The transferred torch creates an electric arc between the tip of the torch and either a metalbath or the conductive lining of the reactor vessel wall. In a non-transferred torch, the arc is
produced within the torch itself. Plasma gas is fed into the torch, heated, and then exits
through the tip of the torch.
There are several approaches to the design of plasma gasification reactors. In one approach,
developed by Westinghouse Plasma Corporation (plasma torch manufacturer) and Hitachi
Metals (plasma gasification system developer and user), a medium pressure gas (usually air
or oxygen) flows through a water-cooled, non-transferred torch, outside of the reactor. The
hot plasma gas then flows into the reactor to gasify the MSW and melt the inorganic
materials.
Another design is an in-situ torch, where the plasma torch is placed inside the reactor. This
torch can either be a transferred or non-transferred torch. When using a transferred torch, the
electrode extends into the gasification reactor and the arc is generated between the tip of the
torch and the molten metal and slag in the reactor bottom or a conducting wall. The low-
pressure gas is heated in the external arc. Alternatively, a non-transferred torch can be used
for creating plasma gas within the torch, which is injected into the reactor.
Several suppliers utilize a completely different approach. In these designs, the reactor is
heated by electric induction coils or an electric arc produced by graphite rods, forming a
molten metal and slag bath. The MSW enters the reactor, where it is subjected to high
temperatures, resulting in partial gasification of the feedstock. From there, the syngas exitsthe reactor. The plasma torch is situated either in a secondary reactor or in a recycle line,
which goes back to the first reactor, assuring complete gasification of the feedstock.
Proponents of the in-situ torch claim its advantages include better heat transfer to MSW and
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The first two approaches have been applied to small-scale commercial waste and medicalwaste processing units. The throughput of the largest external system is approximately four
tons/hour and the throughput of the largest internal system is approximately ten tpd. The
Westinghouse/Hitachi design has been scaled up to 83 tpd per reactor at Utashinai, Japan,
which treats a combination of MSW and auto shredder residue.
Plasma arc gasification typically occurs in a closed, pressurized reactor. The feedstock enters
the reactor, where it comes into contact with the hot plasma gas. In some designs, severaltorches arranged circumferentially in the lower portion of the reactor help to provide a more
homogeneous heat flux. When used for gasification, the amount of air or oxygen used in the
torch is controlled to promote gasification reactions.
Syngas can either be burned immediately in a close-coupled combustion chamber or boiler,
or cleaned of contaminants and used in a reciprocating engine or gas turbine. In the first
approach, the exhaust gases are cleaned after combustion, in an emission control system. Hot
gases flow through the boiler, creating steam used for power generation in a conventional
steam turbine. In the second approach, the syngas is cleaned before it enters the engine or gas
turbine.
As noted above, the primary solid output from plasma facilities is a glassy slag, the result of
melting the inorganic fraction of the waste. Any waste processing facility generating an ash
or slag is required by the United States Environmental Protection Agency (USEPA) to
subject it to a Toxicity Characteristic Leaching Procedure (TCLP) test. The TCLP test is
designed to measure the amount of eight elements that leach from the material being tested.
Data from existing facilities, even those processing highly hazardous materials or medical
waste, show results that are well below regulatory limits.
While there are only a few plasma torch manufacturers, there are over a dozen companies
that have taken the plasma technology and are developing it for use in MSW gasification.
This has led to several suppliers claiming the same operational experience; i.e., severalsuppliers that incorporate Westinghouse plasma torches claim the experience in the Hitachi
Metals plants as being their own or representative of how their system would perform.
2.2.4.2 Throughput
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2.2.4.4 Byproducts
Byproducts of plasma gasification are similar to those produced in high-temperature
gasification, as noted above. Due to the very high temperatures produced in plasma
gasification, carbon conversion nears 100%.
2.2.4.5 Environmental Issues
With regard to air emissions and other environmental issues, the most importantenvironmental issue for gasification, the discussion in Section 2.2.2.5 applies here as well.
2.3 PHYSICAL PROCESSING TECHNOLOGIES
2.3.1 Refuse Derived Fuel
2.3.1.1 Process Description
Figure 2-8 presents a typical process description for a Refuse Derived Fuel (RDF) system.
FIGURE 2-8
TYPICAL RDF SYSTEM
Dryer
Raw MSW
Metals
Glass
Paper
Plastics
Separation of
Recyclables
Moisture
Sizing
ShreddingDensification
Pelletized
RDF
RDF
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The RDF process typically includes thorough pre-separation of recyclables, shredding,drying, and densification to make a product that is easily handled. Initial processing includes
field-based manual picking and removal of white goods and other large ferrous materials.
Glass and plastics are removed through manual picking and by commercially available
separation devices commonly found in Material Recovery Facilities (MRFs). This is
followed by shredding to reduce the size of the remaining feedstock to about eight inches or
less, for further processing and handling. Magnetic separators are used to remove ferrous
metals. Eddy-current separators are used for aluminum and other non-ferrous metals. Theresulting material contains mostly food wastes, non-separated paper, some plastics
(recyclable and non-recyclable), green wastes, wood, and other materials. Reduction of about
50% of the inlet MSW feed can be accomplished through initial RDF processes.
Drying to less than 12% moisture is typically accomplished through the use of forced-draft
air. Steam from an adjacent boiler can be utilized if RDF is being combusted on-site in a
waste-to-energy facility. Additional sieving and classification equipment may be utilized toincrease the removal of contaminants. After drying, the material often undergoes
densification processing such as pelletizing or cubing to produce a pellet or cube that can be
handled with typical conveying equipment and fed through bunkers and feeders.
The RDF can be immediately combusted on-site or transported to another facility for burning
alone, or with other fuels. The densification is even more important when RDF is transported
off-site to another facility, in order to reduce volumes being transported.
2.3.1.2 Throughput
Existing systems operate at an extremely high throughput, typically with several lines each
can be rated at 1,000 tpd.
2.3.1.3 Feedstock Characteristics
Raw MSW is used as the feedstock to RDF plants. Removal of large appliances, batteries,
and other items is required so that downstream equipment as described below can be
operated efficiently.
2 3 1 4 Solid Byproducts
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concern would be the control of fugitive dust (PM10) generated from the mechanicalequipment during the materials separation process and the generation of potential odors.
Because of the fugitive nature of these emissions, the most effective emissions controls are
minimization of mechanical drop distances, adequate ventilation, and capture of emissions
from handling points and effective emissions controls, using baghouse filtration systems and,
if necessary, activated carbon systems for organic and odor emissions abatement.
RDF systems are typically quite large in throughput. Therefore, an important environmentalissue is traffic impact due to the number of trucks delivering MSW. Other environmental
issues associated with RDF systems typically involve nuisance issues such as noise and litter.
2.3.2 MSW Handling Processes
There are many processes for handling MSW. These processes are common in transfer
facilities and MRFs. Similar processes are employed for preparing conversion facility
feedstock for treatment.
2.3.2.1 Drying
A wide range of drying technologies is commercially available, including:
Rotary dryers
Rotary kilns
Fluid bed dryers
Dryers can use steam or a combustion source such as firing diesel oil or natural gas for direct
contact drying. Indirect contact drying, using a heat exchanger, allows for a wide range of
heat sources that do not come into contact with the MSW, although the result tends to be less
efficient than direct contact drying. Dryers are commercially available and single dryers can
be installed in parallel to process several thousand tpd.
2.3.2.2 Mechanical Separation
Mechanical separation is utilized for removing specific materials or contaminants from the
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Trommel screens
Sieves
Grizzlies
Vibrating screens
Centrifuges
Air classifiers
Magnetic separators (for ferrous materials)
Eddy-current separators (for non-ferrous materials)
2.3.2.3 Size Reduction
Size reduction is often required to allow for more efficient and easier handling of materials,
particularly when the feed stream is to be used in follow-on processes. These processes help
to isolate contaminants and specific materials, particularly large appliances and tires. Sizing
processes include passive, moving, and vibrating screens, trommels, and grizzlies. In order to
reduce the size of the entire stream, or portions of it, mechanical equipment, such as
shredders, is utilized. This allows for other physical processes, such as dryers, magnetic and
eddy current separators, and densification equipment to work more efficiently. Magnetic and
eddy current separators may be installed both up- and down-stream of shredders to increase
the recovery of metals.
2.3.2.4 Densification
A wide range of commercially processes and equipment are available for densification.
These processes can be part of an RDF facility, as described above, or used separately for the
preparation of MSW into a more easily handled feedstock. Densification processes include:
Pelletization
Cubing
Extrusion
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All of these processes are well proven in other industries for metallurgical, animal andmedical wastes, agricultural products, biomass, and minerals, as well as RDF production.
These densification processes can easily be used with MSW. As long as the MSW undergoes
some type of pre-processing to remove metal and glass, some plastics can be handled.
Product sizing and form are dependent on the technology chosen. For example, pelletization
may result in short, long, small, or large pellets. Disc agglomerators form round to oval
pellets, with size dependent on feed characteristics and moisture content.
2.3.2.5 Steam Processing/Autoclaving
Several technologies are available for steam processing and autoclaving MSW. A typical
process is shown in Figure 2-9. Steam Processing takes raw MSW (or MSW with minimal
processing) and subjects it to low or medium pressure steam in a closed, rotating pressure
vessel. The high-temperature steam breaks down cellulosic materials and sterilizes the entire
feed stream. The product material exits the steam pressure vessel or autoclave as a recyclable
or usable fiber, which can be used for:
Fiber board
Door and wall paneling
Insulation
Roofing tiles and shingles
FIGURE 2-9
TYPICAL STEAM PROCESSING/AUTOCLAVE PROCESS
Physical
SeparationProcesses
Raw MSW
Autoclave
Sterilized Cellulosic Fiber
De-Labeled Cans and BottlesVolume Reduction ~ 1/3
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Cans and bottles are de-labeled. Plastics typically are slightly melted, resulting in significantvolume reduction.
The MSW stream is reduced in volume by about one third. From there, the sterilized product
can be further processed using one or more of the physical processes described above. Some
processes take the autoclaved product to pyrolysis or gasification.
Existing systems typically load 25-30 tons at a time, and process it for 30-45 minutes. With
loading and unloading time, an autoclave can process about 15