Thermal Conversion of Solid Waste

1
Thermal Conversion of Solid Waste

• Greener Solid Waste Practices An Environmental
  Sustainability Program Davis, California
  (September 17-18, 2007)

G.M. Savage, L.F. Diaz, and L.L. Eggerth
CalRecovery, Inc. Concord, California
USAGSavage_at_calrecovery.com
2
Outline

• Some Important Concepts
• General Types of Thermal Technologies
• Overview
• International
• USA
• Conclusions

3
Introduction

• Focus of presentation
• description of some thermal technologies that
  have been demonstrated and some that are under
  development
• presentation is a high level overview only

4
Thermal Processes

• Direct combustion (CH O2 ? CO2 H2O)
• Pyrolysis (thermal process occurs in the absence
  of O2/air)
• Gasification (sub-stoichiometric air)
• Plasma arc (very high temperature gas)

5
Example of Typical California Solid Waste
Management Infrastructure Designed to Achieve
High Waste Diversion Rates
Yard Waste,Wood Waste,Concrete, Kraft Paper
90
80
70
Food Waste
60
Diversion from Disposal ()
50
Paper Containers
40
Food Waste
30
Mixed Paper
20
Yard Waste
10
Containers Newspaper
0
Residential
Commercial
Construction Demolition/Self-Haul
High
Low
Degree of Municipal Control
6
Examples of Recovering Energy from Solid Wastes
Steam
Steam Boiler and Turbine/ Generator
Direct Combustion
Electricity
Fuel Materials (e.g., wood, crop residues)
Source-SeparatedOrganics
Ash
Medium- or High-Quality Fuel Gas
Pre-Processing (i.e., front-end) (mechanical
and/or manual)
Biogasification/ Anaerobic Digestion
Sludge
Low-/Medium- Quality Fuel Gas
Non-combustible Process Residues
Thermal Gasification/ Pyrolysis/Liquefaction
Fuel Materials (e.g., paper, food)
Char
Liquid Fuel/Residue
Pre-Processing (i.e., front-end) (mechanical
and/or manual)
Mixed MSW
Steam
Fluidized Bed Combustor
Steam Boiler and Turbine/ Generator
Electricity
Ash
Non-combustible Process Residues
Recyclables
Liquid Fuel
Ethanol Production
Residue
7
Comparison of Solid Waste Characterization
Worldwide ( wet wt)
a Includes briquette ash (average). b Includes
all others. c Includes small amounts of wood,
hay, and straw. d Includes garden waste.
8
Comparison of Thermal Characteristics of MSW and
Those Needed for Self-Sustained Combustion
100
90
10
80
20
70
30
60
40
Moisture Content ()
Ash ()
50
50
40
60
30
70
20
80
10
90
100
10 20 30 40 50 60 70 80
90 100
Volatile Solids ()
Area of Self-Sustained Combustion
Typical Values for Many Industrialized Countries
Typical Values for Developing Countries
9
Type of Treatment of MSW in Europe (2004)
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European Union

• Recent legislation regarding SWM the Landfill
  Directive
• bans disposal of untreated organic materials into
  landfills

11
Targets for Biodegradable Waste Diversion
(Landfill Directive) in the EU
The directive allows for a 4-year derogation
for Member States that were landfilling more than
80 of the biodegradable waste in 1995
12
WTE in the EU

• 50 million tons of MSW thermally treated in
  420 plants produced - 20 million MWh of
  electricity
• - 50 million MWh of heat
• In 2005, 13 countries produced 12.7 million
  tons of RDF or SRF

13
Fundamentals of Modern Waste Incineration (EU)
filter
Recovery of Cl, Br, Hg, gypsum
Inertization disposal (storage)
Utilization
Source Vehlow, J. Germany
14
Management of Boiler and Filter Ash in Europe

• Extraction/sintering
• Fusion/vitrification
• Stabilization
• Filler in asphalt (NL)
• Utilization in salt mine (D)
• Storage for future use

Source Vehlow, J., 2006
15
MSW Management in the United States (2003)
Source US EPA
16
Number of Waste-to-Energy Facilities in the
United States (1982 to 2004)
Source 2005-2006 Municipal Waste Combustion in
the United States, 8th Edition, E.B. Berenyi
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Thermal Gasification/Pyrolysis System Schematic
Pyrolysis (syn) gas
Organic Feed
Pyrolysis Reactor
Pyrolytic Oil
Char (e.g., carbon black)
Heat
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Gasification

• Carbon in waste or biomass reacts with steam and
  oxygen (from air) at sub-stoichiometric
  conditions
• Primary reactions
• C O2 -gt CO2 (exothermic)
• C H2O -gt CO H2 (endothermic, water gas)
• C CO2 -gt 2 CO (endothermic)
• CO H2O -gt CO2 H2 (exothermic, generator gas)
• Resulting synthesis gas (syngas) can be used for
• energy production in IC engines or turbines
• synthesis of chemicals
• hydrogen production

19
IC Engine Firing Syngas
Gasifier (rt) and Gas Conditioner (lt)
Engine and Dynamometer
20
Gasification as Front-end Plant
Source Bilitewski, B., 2006
21
Pyrolysis

• Endothermic reaction of organic fraction of
  waste, biomass, or liquid waste in the absence of
  oxygen at high temperature and pressure
• Organic matter is transformed to a gas, liquid,
  and a solid (char)
• Temperature and pressure levels affect the
  relative ratios of gas, liquid, and solid

22
Thermal Gasification/Pyrolysis

• Several pilot plants have been operated
• Reliability and maturity of the technology has
  not been demonstrated at full-scale
• Major issues deal with solid residues produced,
  gas clean-up, quality of liquid fuel, and air
  emissions

23
Pyrolysis (or Gasification) and Melting System in
Japan
Melting
Gasification
Slag
SourceMatsuto, T.
24
Slag and Metal in Japan
About 150 melting systems in operation in 2002 in
Japan
Source Matsuto, T.
25
Fischer-Tropsch (FT) Process

• Proven technology, originally invented in Germany
  in 1920s
• Catalyzed chemical reaction where hydrogen and
  carbon monoxide are converted to liquid
  hydrocarbons
• Typical catalysts based on Fe and Co
• Main objective is to produce a synthetic
  substitute to petroleum

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Plasma Arc

• Energy that is added causes neutral atoms of gas
  to split (5,000 to 10,000 degrees C)
• As atoms split a plasma of positively and
  negatively charged atoms and electrons is formed
• Need high voltage to generate electric arc, two
  electrodes (cathode and anode) and gas (helium,
  air)

27
Plasma -- Commercial Applications

• Welding and cutting
• Steel melting furnaces
• Some hazardous and radioactive wastes treated

28
Plasma -- Application to SW

• Small unit operating in a cruise ship for about 3
  years
• Some propose to gasify the waste and use gas to
  generate electricity
• Several start-up companies during the last few
  years, most operate pilot plants
• Concerns about gas cleaning and solid residue
  produced
• Unproven on commercial scale in United States

29
Plasma -- Application to SW

• One or two facilities operating in Japan
• One facility in Utashinai, Japan processes a
  fraction (segregated) of residential waste mixed
  with ASR
• Gas produced is burned in a boiler to produce
  steam and generate electricity with a steam
  turbine

30
Plasma -- Application to SW in Japan
Facility in Utashinai, Japan
31
Plasma -- Application to SW in Japan
Facility processes a selected fraction of
residential waste and ASR
32
Plasma -- Application to SW in Japan
Main reactor
Partial view of processing facility
33
Plasma -- Application to SW in Japan
Steam turbine
Slag removal
Solid residue
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Conclusions

• Direct combustion (massburn)-- well developed,
  substantial history many systems producing
  steam/electricity
• Fluidized bed -- under development, sporadic
  history interest is primarily a function of
  fossil fuel prices and air pollution regulations

35
Conclusions (cont.)

• Thermal gasification -- under development,
  sporadic history interest is a function of
  fossil fuel prices
• With current emphasis on sustainability, highest
  and best use of materials, and system
  integration, a number of design
  criteria/conditions must be considered when
  planning and implementing energy recovery from
  waste