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• Overview of waste management • Waste to Energy Technologies
– Thermal treatment – Biological treatment – Physical treatment
• Policy perspective
Solid Waste (SW)
/Municipal Solid Waste (MSW)
• SW means any garbage, refuse, sludge and other
discarded materials, resulting from industrial,
commercial, mining and agricultural operations, and from
community activities • MSW—more commonly known as trash or garbage—
consists of everyday items we use and then throw away, such as product packaging, grass clippings, furniture, clothing, bottles, food scraps, newspapers, appliances,
Sources of Solid Waste
• Residential area • Market and
Restaurant • Commercial and
Department Store • Institutional area • Industrial area • Agricultural area
Waste Management
Waste management is the collection, transport, processing, recycling or disposing, managing and monitoring of waste materials. The term usually relates to materials produced by human activity, and is generally undertaken to reduce their effect on health, the environment or aesthetics. Waste management is also carried out to recover resources from it.
Waste management concepts
• Waste hierarchy - extracts the maximum practical benefits from products and to generate the minimum amount of waste.
• Extended Producer Responsibility (EPR) is a strategy designed to promote the integration of all costs associated with products throughout their life cycle (including end-of-life disposal costs) into the market price of the product.
• Polluter pays principle (PPP) is a principle where the
polluting party pays for the impact caused to the
environment. With respect to waste management, this
generally refers to the requirement for a waste generator to
pay for appropriate disposal of the waste.
Hierarchy in Solid Waste
Management
1. Waste Avoidance Most desirable 2. Waste Minimization - CT 3. Waste Reuse/Recycling 4. Waste Treatment 5. Waste Disposal Least desirable
Note: Complete avoidance of solid waste generation is not possible
in real world. Not all wastes are technically and economically
feasible to be recycled or treated. Therefore, final disposal is
still required as an essential part of the management at the end
of integrated solid waste management system.
Structures of Municipal Solid Waste Stream Western Countries
Prolonged emission of
Plastic
resource
Metals
(Incineration)
Waste
Mechanical Separation
Landfill LFG recovery
Collection
+Aerobic Treatment
Separation after collection
(Mechanical-Biological Treatment) Incomplete reduction of organics MBT
“Mechanical Separation” should be applicable to waste with low water content.
Japan
Paper, Metals, Glass, Plastic resource
Combustibles Substantial reduction of organics
Waste
Sourc e
Landfill
Collection
Incineration
Separation
Few CH4 emission
Separation before collection
Uncombustibles
“Incineration” has been selected due to sanitation of waste with high water
content. Asian Countries Resource
Organics is still valuable
Waste Collection Landfill
Waste situation in Asia
• In Asia, on an annual basis, approx. 4 billion tonnes of solid
waste are generated and MSW amounts to 790 million tonnes. • About USD25 billion are spent for solid waste management
in urban areas.
• On average 50% of residents lack collection services in urban
areas of low and middle income countries
MSW management in Asia • Municipal solid waste composition varies broadly due climatic
and cultural variations (about 50% is biodegradable) • Systems for collection, transportation and disposal are similar • Involvement of formal (public and private organizations) and
informal sector, NGOs and community based organizations, etc. • Industrial waste (hazardous and non hazardous waste) enters the
MSW stream • Disposal of waste electric and electronic equipment
(WEEE) to landfill
Key Features of Integrated Waste
Management (IWM) concept
An overall approach Uses a range of collection and treatment
methods Handles all materials in the waste stream
Environmental effective Economical affordable Socially acceptable
Anticipated Solid Waste Management Condition in
the Future
1. More stringent regulation 2. Increasing public opposition against facility siting 3. Increasing cost of waste transportation
IWM could help reducing the cost 4. Centralization of waste management facilities
Economically driven
Facing Problems in SWM
1. Limited allocated budget for solid waste management 2. Lack of co-operation between local authorities 3. Lack of skill personnel in waste management practice 4. Ineffective waste recycling program/regulations 5. Opposition against waste disposal facilities from
public/communities 6. Lack of public awareness/participation
Waste is not waste
• Waste is a misplaced resource • Waste residues can be converted into
reusable/new materials, energy, and other
products with value • Natural resources are limited and depleted • Mitigation of waste management problems • Waste can be potential sources for resource
recovery
Waste to Energy Quote The old practice of waste disposal has been to dump in
open landfills, which results in garbage in and garbage remains.
The goal for the new millennium must be garbage in and
energy out in an environmentally acceptable manner.
Thermal Treatment of MSW
• Incineration (energy recovery through complete
oxidation): mass burn and RDF • Pyrolysis • Gasification • Plasma arc (advanced thermal conversion)
Incineration of Solid Wastes
Incineration is a thermal processing used for reducing volume of solid wastes and recovering energy. In the process, solid wastes are converted into gaseous, liquid and solid conversion products under high temperature (800-1,000° C), with the concurrent or subsequent release of heat energy.
Terms
Burn: to produce flames and heat
Combustion: a chemical process in which
substances combine with the oxygen in the air to
produce heat and light.
Incinerate : to burn something until it is
completely destroyed
Change of requirements to
Incineration disposal technology
Functions and roles widely required in
incineration treatment have changed in response to
the needs of the times…
1950~
Appropriate treatment for sanitation Basic matter
Weight reduction→ 1/10
Weight/volume reduction
Volume reduction→ 1/20 1980~
HCl, Dioxins, NOx… Reduction of environment impacts
2000~
Energy from waste Recycling and resource recovery
Thermal recovery
Potential and limitations of
incineration technologies
Potential
Energy recovery from organic wastes Small footprint Only long-term solution for large cities/municipalities Volume and weight reduced (approx. 90% vol. and 75%
wt reduction) Cost can be offset by heat recovery/ sale of energy
Limitations High investment and operating cost Strong opposition from the public/stakeholders Skilled operators are required
Pros
• Over 900 plants • Over 10 major suppliers • adequate tender competition • Larger unit capacity • less land requirement • Relatively robust for mixed MSW treatment • No requirement of pre-treatment
Cons
• Excess air requirement higher flue gas volume
• High ash production Latest Development
• Over 90% of MSW incineration plants using moving grate technology • Largest plant: 4,300 tpd mixed MSW in Singapore • Largest unit : 920 tpd mixed MSW in Netherlands • Over 100 new plants since 2003
Incineration – Fluidized Bed Latest Development • Mainly for homogenous waste treatment e.g.,
sewage sludge and industrial wastes • Only 2% of mixed MSW incineration plants using
this technology • Largest plant: 200 tpd mixed MSW in Japan • Largest unit: 82.5 tpd mixed MSW in Japan • A few new MSW plants since 2003, but in small
scale Pros • More intense heat and mass transfer • Minimal mechanical moveable parts less
wearing and lower relevant O&M costs Cons • Limited track record for mixed MSW application • Smaller unit capacity larger land requirement • Requirement of pre-treatment • Less robust for mixed MSW treatment
Incineration – Rotary Kiln Latest Development • Mainly for industrial and hazardous
waste treatment, rare for mixed MSW • Generally, combine rotary kiln and moving grate • Largest plant: 900 tpd mixed MSW in Taiwan • Largest unit: 300 tpd mixed MSW in Taiwan • No reported new plant since 2003 • Long retention time favorable to
treat hazardous waste • Flexible in feedstock e.g., solid and liquid wastes Cons • Limited track record for mixed MSW
application/ a supplier key retreated from market
• High O&M costs due to technical problems
encountered for mixed MSW treatment such as erosion of the refractory materials, plastics deposition and clinkering
• Smaller unit capacity larger land requirement
• Less robust for mixed MSW treatment
Energy recovery
• Hot water boiler • Low pressure
steam boiler • High pressure
steam boiler • Electricity • Co-generation
Gasification
Partial oxidation process using air, pure oxygen, oxygen enriched air, hydrogen, or steam
Produces electricity, fuels (methane, hydrogen, ethanol, synthetic diesel), and chemical products
Temperature > 700oC
More flexible than incineration, more technologically complex than incineration or pyrolysis, more public acceptance
Gasification Latest Development ~90 plants worldwide
Largest plant: 405 tpd mixed MSW in Japan Largest unit: 150 tpd mixed MSW in Japan Over 20 new plants since 2003, but
in small-scale Limited air requirement less volume
of flue gas for treatment
Potentially higher flexibility in energy recovery Cons
Limited track record for mixed MSW application/ a key supplier retreated from market
Concern for operation failure (e.g. unpleasant experience in Germany)
Smaller unit capacity larger land requirement
Less robust for mixed MSW treatment Requirement of pre-treatment
Pyrolysis
Thermal degradation of carbonaceous materials Lower temperature than gasification (750 –
1500oF) Absence or limited oxygen Products are pyrolitic oils and gas, solid char Distribution of products depends on temperature Pyrolysis oil used for (after appropriate post-
treatment): liquid fuels, chemicals, adhesives, and other products.
Plasma Arc
Latest Development ~30 pyrolysis plants Largest plant: 160 tpd mixed MSW in Japan Largest unit: 80 tpd mixed MSW in Japan Less than 10 new plants since 2003
Temperatures 4,000°C to over 7,000 ° C
Hazardous & toxic compounds broken down to elemental constituents by high temperatures
Organic materials are converted
to fuel gases
Residual materials (inorganics, heavy metals, etc.) immobilized in a rock-like vitrified mass which is highly resistant to leaching
Comparison among Incineration,
Gasification, Plasma Gasification & Pyrolysis
Criteria Moving grate Gasification Pyrolysis
Environmental Factors
Flue gas volume High Medium Low
Ash production High High Medium
Engineering Factors
Flexibility Good Poor Poor
Track Record/Operation Experience Longest Limited Limited/Rare
Reliability - Treatment capacity Largest Medium to small Small
No. of key supplier Many Limited Rare
Land requirement Low Medium Large
Capital and O&M cost Low High High
Biodegradable waste
• Biodegradable waste is a type of waste which can be broken down, in a reasonable amount of time, into its base compounds by micro-organisms and other living things.
• Biodegradable waste can be commonly found in municipal solid waste (sometimes called biodegradable municipal waste, or BMW) as green waste, food waste, paper waste, and biodegradable plastics. Other biodegradable wastes include human waste, manure, sewage, and slaughterhouse waste. In the absence of oxygen, much of this waste will decay to methane by anaerobic digestion.
Type of biological treatment process • Aerobic Composting
– Need more space and time consuming – More energy & manpower required – O&M problems – Odor problems, high moisture content of waste
• Anaerobic Digestion – Higher net power generation – Lesser plant area required for a continues operation – Greater volume reduction in MSW – Organic stabilization and pathogen reduction
Bio-methanization may be the attractive alternative in Asian countries where higher organic fraction exist.
Anaerobic Digestion of Solid Wastes
The biodegradation of organic wastes by microorganisms
under anaerobic conditions in anaerobic digester will give
final products as biogas (mixture of methane and carbon
dioxide) and anaerobic sludge.
Technology options: - One-stage anaerobic digestion system
Wet process 10-15% TS Dry process 20-40% TS
- Two-stage anaerobic digestion system - Batch system
DRIVING FORCES BEHIND THE GROWTH OF
ANAEROBIC DIGESTION OF ORGANIC WASTE
• Introduction of Bio-waste collection
• Incentives for production of renewable energy • Sustainable plants ‘win’ more municipal waste procurements
• Advantages of AD – Economically very attractive – No excess wastewater for dry systems: partial
stream digestion – More waste can be treated on the same surface area – Reduction of odors – Hygienization: important for food waste – High flexibility
Potential and limitations of AD technologies
Potential
- Recovery of energy from solid wastes - Simple operation and maintenance (compared
to incineration) - Utilization of organic residue as compost
Limitations
- High investment cost (for large scale AD) - Difficulties in preparation of feedstock (poor upstream management)
How is biogas produced? Biogas occurs widely in nature. Biogas
forms wherever organic material accrues
under exclusion of oxygen (called anaerobic
digestion), e.g. in bogs, on the bottom of
lakes or in ruminants’ stomachs. The organic
matter is almost entirely converted into
biogas in these conditions. The actual
process by which biogas forms involves the
complex interaction of various
microorganisms and takes place in basically
four separate phases
End product = Biogas Composition:
50 – 75 % methane (CH4)
25 – 45 % carbon dioxide (CO2) 2 – 7 % water (H20) < 2 % oxygen (O2)
< 2 % nitrogen (N2) < 1 % ammonia (NH3)
< 1 % hydrogen sulphide (H2S)
The energy content of the biogas is directly dependent on the methane content.
The higher the content of substances such as fats and starch that are easy to break down in the fermented mass, the greater the gas yield.
One cubic meter (m3) of methane has an energy content of about ten kilowatt hours (9.97 kWh).
If the biogas contains 60 % methane, then the energy value of one cubic meter of biogas is about six kilowatt hours. In this case, the heating value of one cubic meter of biogas is roughly 0.6 liters of heating oil.
50
Energy equivalents • 1 Watt = 1 joule second-1 • 1 Wh = 1 x 3600 joules (J) • 1 kWh = 3600000 J • 1 kWh = 3.6 MJ • 22 MJ (1m3 biogas) = 22/3.6 kWh = 6.1 kWh • Electrical conversion efficiency = 35% • Therefore 1m3 biogas = 2.14 kWh (elec)
To get a good combustible gas, the “raw” biogas is cooled, drained,
dried and cleaned from H2S because of its corrosive effect. The obtained gas can be either applied directly or upgraded to natural gas standard – biomethane (98 % methane).
Biogas:
• Production of electricity and heat (cogeneration) • Production of electricity alone • Production of heat alone
Upgraded biogas (biomethane):
• Injection in the gas grid
• Transportation fuel
• High tech process energy
• Raw material for the chemical industry
Differentiation Wet and Dry
Fermentation • Wet fermentation DM-content of the substrates does not exceed 15 % Pumpable substrates or mixtures Usually continuous processes
• Dry fermentation DM content exceeds 15 % (DM contents of 35%
or more can occur Stackable substrates or mixtures Usually discontinuous processes
Advantages and disadvantages of
Different systems
One Stage System Two-stage system
Continuous
system
Advantages Simple, low-tech, Process stability, Could treat large
cheap, smaller reliable process, amount of waste
heat requirement higher biogas
yield,
Disadvantages Clogging, need Higher cost of Low process
bulking agent, risk investment, efficiency, poor
of explosion complex biogas yield
during emptying a operation,
reactor, poor expensive waste
biogas yield handling
equipment
Mixing Options
• Passive mixing due to thermal convection • Active mixing
– Mechanical mixing systems • Reel agitator • Paddle agitator
– Propeller agitators • Submersible motor propeller
agitator • Tube screw pump
– Hydraulic circulation • Circulation pump
– Circulation by biogas • Active systems (gas injection)
• Passive systems (pressure balance)
Conclusion
A basic requirement for successful implementation of WtE is the
existence of an advanced waste management system which is
based on the separate collection and treatment of different source
separated waste streams. Bio-mass such as kitchen and garden
waste are digested and/or composted. Recyclables such as paper,
card-board, PET, glass, metals etc. are sorted and directed to the
recycling industry. The management of hazardous waste is
controlled. Remaining MSW fractions which cannot be recycled
are disposed of in a controlled landfill. International experience indicates that the implementation of state
of the art co-processing and landfill gas collection can be
successful if a systematic waste collection exits and some selected
waste streams such as tires or biomass can be directed to the
facilities. Anaerobic digestion requires separate collection of
biomass because any contamination with other MSW fractions
may cause problems with the process and the use of the diges-tion
residues in agriculture. On this waste management level the
suitability of incineration should be assessed in detail before a
project is initiated - some improvements of the waste management
system might be required.
***End***
Thanking You
RPG Group
Raymond Tech Australia
155A, March Street, Richmond Sydney, NSW 2753,Australia
Email: [email protected]
www.pillaygroup.com.au