Chapter----five---Resource Recovery.pptx

SOLID WASTE@PULCHOWK CAMPUS
Resource Recovery
Group members:
Sajan Dangi, 132
Sambodhan Sharma, 133
Sandesh Tiwari, 141
Sanjay Gamuwa Tharu, 143
Tutor:
Assoc Prof. Shukra Raj Paudel
Department of Civil Engineering
Pulchowk Campus
IOE, Tribhuvan University
2022-06-16

SOLID WASTE@PULCHOWK CAMPUS 2
Content
5.1 Introduction to Resource Recovery
5.2 Material Separation and Processing Techniques
5.3 Material Recovery Facilities
5.3.1 Unit Operation in MRF
5.4 Conversion Technology for Recovery
5.5 Biological Conversion
5.5.1 Composting, Vermicomposting
5.6 Recovery of Thermal Conversion Products
5.6.1 Incineration, Types and Design Consideration, Environmental
Consideration

Scope of this presentation
 I. To give clear concept about materials separation and processing techniques.
 II. To shed light upon various materials recovery facilities.
 III. To explain about the Biological conversion and technology use for recovery.
 IV. To explain about the recovery of chemical conversion products.

5.1 Introduction
 Resource recovery is a process of recovering energy and reusable materials
from solid waste before their decomposition in landfill.

Introduction
Energy Recovery :- Conversion of non-recyclable
materials into usable heat , electricity or fuel
including the procedure of combustion,
gasification, pyrolization , anaerobic digestion
e.t.c .

Differences Between Pyrolysis and Gassification
 Pyrolysis is the process of thermal conversion of organic matters using a
catalyst in the absence of oxygen , whereas, gasification is the process of
thermal conversion in the presence of oxygen.
 Temperature in pyrolysis process is 3500
– 6000
C ,whereas, 8000
– 12000
C in
gasification process.
 Pyrolysis is used in ethylene production to treat plastic waste,fuel from
biomass wheras gasification is used for heat and electricity production.

Importance of Resource Recovery
When complete avoidance and reduction of waste are not possible, resource
recovery is most important.
 It helps to extract all recoverable materials for reuse and recycling.
 By burning the solid waste into ash, it reduces the volume of waste entering
the landfill by 90% and recovers valuable energy.
 Revenues can be collected by selling the resulting energy to local electric
companies.

Principle of 3R

Reduce
Reduce the usage of materials to the extent
possible. Go for the alternative resources that
can replenish themselves without affecting
our environment.

Reuse
 Once the materials are used for the primary purposes, reuse them for some
secondary purposes.

Recycle
 Recyling of the materials can be done until their properties are useful and are
not degraded to an extent that can prevent their effective use.

Differences Between Recycle and Reuse
 Recycle is the process of turning into raw materials and completely a new
products is formed whereas reuse refers using an object without any special
treatment.
 Recycle is energy consuming procedure whereas reuse helps to reduce
pollution .

5R

5R(Reject,Reuse,Reduce,Repair,Recycle)
 Reject single use plastics. If a synthetic material must be used, make sure it
can be reused multiple times.
 Employ proper packing techniques to ensure the reuse of the materials.
 Reduce the usage of materials.
 Store materials that needs to be repaired and adopt for future use.
 Recyling of the materials can be done until their properties are useful.

7R Principle of MSW

7R Principle of MSW
 Recycle
 Refuse
 Reduce
 Reuse
 Repair :- Instead of throwing out your good shoes – take them to a boot maker
and have them resoled and reheeled.

7R Principle of MSW
 Re-gift :-When the kids grow out of their clothes or have out grown their toys,
hand them on to friends and family or take them to the shop. You could even
make some money while helping the environment by selling unwanted items
on ebay.
 Recover :- Shred or chip your prunings and use them on your garden – it will
add much needed carbon to your soil and save water. Why not hire a shredder
for the day – you could share the cost with a neighbour or two!

Separation of Solid Waste
 Separation :- The segregation of different types of solid waste at the location
where they are generated (a household or business).

Processing of Solid Waste
 Processing :- An operation for the purpose of modifying the characteristics or
properties of solid waste to facilitate transportation or disposal of solid
wastes including incineration, depositing, separation, grinding, shredding, and
volume reduction.

Processing of Solid Waste

Transformation of Solid Waste
 Transformation :- Incineration of solid waste to produce heat or electricity.
Importance of Transformation :-
 To improve the efficiency of solid waste management system.
 To recover reusable and recoverable materials.
 To recover conversion products and energy.

Importance and Necessity of Separation of MSW
 Saving on disposal cost .
 Reduction on the quantity of solid waste that need to be transported on
landfill site.
 Saving on transportation cost.
 Increased recycling rate.
 Less impact on Environmental quality.

Types of Separation
There are two types of separation of solid waste:-
a) Manual Separation :- The separation of
recyclable or compostable materials from
waste by hand sorting.

Types of Separation
b) Mechanical Separation :- Separation of solid waste with the help of
mechanical means.

Types of Manual Separation
 Waste separation at the source of generation :- Waste separation at the
source is usually done by manual means. The number and types of
components separated will depend on the waste diversion goals established
for the programs. Even though waste materials have been separated at the
source , additional separation and processing will usually be required before
these materials can be reused and recycle.

Collection of Waste Separated at source
a) Drop–off centers :- A drop-off program requires residents or business to
separate recyclable materials at the source and bring them to a specified drop-
off or collection centers. Drop-off centers range from the single material
collection points to staffed, multi materials collection centers. Because
residents and businesses are responsible for not only separating their recyclable
materials but also taking them to the drop-off centers, low participation can be
a problem in achieving the diversion rates drsired from these programs.

Drop-off Centers

Collection of Waste Separated at Source
b) Buy-Back Centers :- It refers to a drop-off program that provides a monetary
incentive to participate. In this type of program, the residents are paid for
their recyclable either directly or indirectly through a reduction in monthly
collection and disposal fees. Other incentive system includes contests or
lotteries.

Types of Mechanical Separation of Solid Waste
 Waste Separation at MRFs :- Material Recovery Facility (MRF) is also known as
Material Reclamation Facility or Material Recycling Facility. An MRF is a place
where waste collected from the doorstep in a segregated manner is further
segregated and various components of recyclable waste recovered from it for
recycle or resale.

Types of Mechanical Separation of Solid Waste
MRFs is used for the following tasks :-
 For the further processing of source separated waste obtained from curbside
collection programs and drop-off and buy-back centers without processing
facilities.
 For the separation and recovery of recyclable materials from MSW.
 Improvements in the quality of the recovered materials.

Waste Separation at MRFs
 MRFs for Source-Separated Wastes :- It includes paper and cardboard from
mixed paper and cardboard; aluminum from commingled aluminum; plastics
by class from commingled plastics ; glass by color from mixture of glass.
 MRFs for Commingled MSW :- Wastes are separated both manually and
mechanically. All types of solid wastes can be separated from commingled
MSW.

Importance and Necessity of Processing
 Reduction on transportation cost
 Size reduction of waste
 Reduction on the further impact of solid waste on Environment
 Reduction on the disposal cost of solid waste

Processing Techniques
Size reduction equipment used for the processing of waste includes shredders,
glass crushers and wood grinders .
a) Shredders :- The most three types of
shredding devices are hammer mill, flail mill
and the shear shredder.

b) Glass Crushers :- It is used to crush glass containers
and other glass products found on MSW. Glass is
often crushed after it has been separated to reduce
storage and shipping costs.

c) Wood Grinders :- Typically, most wood
grinders are wood chippers, used to shred
large pieces of woods, which can be used
as fuel and liner materials, which can be
composted.

Material Recovery Facilities(MRF)
 Centralized facility for separation and processing of Solid waste.

Functions of MRF
 To modify physical characteristics of wastes so that waste components can be
removed easily.
 To remove specific components and contaminants from waste stream.
 To process and prepare separated waste for subsequent uses.
 To package the waste for transportation.

Unit Operations in MRF
 MRFs consists of different components or units which have specific tasks and
functions.
 Functions of these units are called unit operations.
Unit operation 1 Unit operation 2 Unit operation 3
Handling Handling
Fig: Skeletal Layout of MRF

List of Unit Operations
 Size Reduction(Shredding, Milling or Grinding)
 Reduce size to obtain reasonably uniform product.
 Screening
 Separation on the basis of size.
 Air Classification
 Separation on the basis of density.
 Magnetic Separation
 Separation of metals from non-magnetic waste
 Densification
 Increase bulk density of waste(compaction)

Unit operation- Size Reduction
 Also called Mechanical size reduction.
 Machines for size reduction:
 Shredders
 Glass Crushers
 Wood Grinders

Size Reduction- Shredders
 Size is reduced by cutting action.
 Used for all types of wastes.
 Some types of Shredders
 Hammer mills
 Flail mills
 Shear Shredders

Shredders- Hammer Mills

Shredders- Flail Mills & Shear Shredder

Size reduction- Glass Crushers
 Size reduction by crushing action.
 Used for Glass wastes.

Size Reduction- Wood Grinders
 Size reduction by grinding action.
 Used for wood wastes.

Unit Operation- Screening
 Separation of wastes into two or more size fraction with the help of screening
surfaces.
 Application of screening in MSW processing:
 Removal of oversized and undersized materials.
 Separation large materials from combusted ashes.
 Separation of grit from combustible materials.
 Separation of paper & plastics from glass & metals.
 Equipment used for screening (Type of screening) are:
 Vibrating screens
 Rotary screens (Trommels)
 Disc Screens

Screening- Vibrating Screens
 Consists of inclined screens and vibration is in vertical motion.

Screening- Rotary Screens(Trommels)
 Trommels are also called rotary drum screens.
 Consist of rotating drum with holes.

Screening- Rotary Screens(Trommels)-continue:
 Materials passing through screen are called under/undersize/underflow.
 Material not passing through screen are called over/oversize/overflow.
 Trommels may be equipped with blades upto first third of length of cylinder.
 Bladed trommels are used for bag breaking.

Screening- Disc Screens
 Consists of rotating parallel horizontal shafts with disc.
 Best type of screening due to:
 Adjustable screening size
 Self cleaning

Unit Operation- Air Classification(Density Separation)
 Used to separate heavy inorganic materials(metals, glass) and light organic
materials(paper, plastics).
 Material mix is introduced into air current of sufficient velocity.

Unit Operation- Air Classification(Density Separation)-contn.
 Dense materials are called heavy fraction and light materials are called light
fraction.
 Stoners are commonly used with trommels.
Fig: Stoner

Unit Operation- Magnetic Separation
 Ferrous metals are separated from other waste using their magnetic property.
 Consists of conveyer belt and magnetic drums or shafts(pulley magnet).

Unit Operation- Magnetic Separation
 Application of Magnetic Separation:
 Separation of tin cans and aluminum cans.
 Separation of ferrous materials after shredding.
 Overhead large magnetic system before shredding (also called scalping).
Fig: Scalping

Unit Operation: Densification
 It is the compaction of solid waste in order to decrease volume.
 Done by following methods:
 Balers : Used for metals, paper and plastics.
 Can Crushers : Used for cans.
Fig: Compacted waste Fig: Compactor

Facilities for Moving Wastes in MRF
 These facilities are used within MRF to move waste from one unit to another.
 Conveyer belt system is used for movement of wastes.
 Slow moving conveyer belt used for manual sorting is called picking belt.
Fig: Trough Belt conveyer Fig: Flat Belt conveyer

Movable Waste Handling Equipment in MRF
 Front end loaders and Forklifts are use to handle the waste.
Fig : Frontend Loader Fig : Forklift

Weighing and Storage Facility in MRF
 Weighing machine is used to measure weight of waste.
 Processed waste is stored in Storage Facility before being sold or transported.

Development and Implementation of MRFs
MRF

Modern Technique of Sorting- Optical Sensor

MRFs in Nepal
 Material Recovery is practiced in every major cities of Nepal by scrap dealers.
 Scrap Dealers buy recyclable and inorganic waste like paper, glass, metals and
sometimes electronic waste from citizens.
 These materials are taken to very primitive MRF for further manual separation
and processing.

MRFs in Nepal

MRFs in Nepal- Electronic Waste Recovery

 MRFs can be build as stand alone facility or can be build in place of transfer
station.
 When MRF is build to act as both Recovery Facility and Transfer Station it is
called MR/TF MR/TF(Material Recovery/Transfer Facility.
 MRF(Material Recovery Facility) & MR/TF(Material Recovery/Transfer Facility)
need following consideration:
 Engineering Consideration( Facility Design Consideration)
 Non Engineering Consideration (Societal, Environmental, Economical
Consideration)

Engineering Consideration
 Engineering Consideration includes:
 Definition of functions of MRF : This includes defining the goal of the facility
considered.
 Selection of material to be processed(now and future): This includes the
type of materials to be processed for maximum benefit cost ratio in present
time as well as in future.
 Identification of material specification : More thorough properties of
materials.
 Development of separation process flow diagram
 Determination of process loading rates
 Modeling and design of layout of facility
 Environmental controls: Temperature, Humidity, Ventilation, Lighting control.
 Aesthetic consideration

Engineering Consideration: Function of MRF
 Function of MRF directly depends on:
 Expected role of MRF in waste management system.
 Type of material to be recovered.
 Form in which waste material will be sent to MRF.
 Containerization and Storage of processed material for the buyers.
 Following Cases will be discussed with flow diagram:
 Typical MRF for source separated waste(Dual Stream)
 Typical MRF for commingled MSW(Single Stream)

Mixed
Paper
Receiving
Area
Manual
Sorting
Manual
Sorting
Bailing
Storage
of Bales
Shipping
Typical MRF for Source Separated Waste
Picking
Conveyer
Front end
loader to
spread
waste
Collection
Vehicle
Conveyer
belt
Forklift Forklift
Bulky items,
Cardboard
Contaminants
Cardboard

Coming-
led glass
and
plastic
Receiving
Hopper
Manual
Sorting
Manual
Sorting
Vibrating
screen
Glass
Crusher
Shipping
Typical MRF for Source Separated Waste`
Conveyer
Conveyer
Collection
Vehicle
Conveyer Conveyer Forklift
Plastic according to
type
Clear glass Residual
material to landfill

Coming-
led
aluminu-
m and tin
can
Receiving
Hopper
Overhead
magnet
Pulley
magnet
Baler Storage Shipping
Typical MRF for Source Separated Waste
Conveyer
Conveyer
Collection
Vehicle
Conveyer Conveyer Forklift
Tin cans crushed Tin can crushed

Biological Conversion
 To convert (transform ) organic fraction into gaseous, liquid, and solid
conversion products, •Compost •Methane •Proteins •Alcohols
 Municipal refuse contains about 75% OM • Which can be converted useful
energy by combustion or other useful products
 The basic objectives of BCP is to convert organic matter OM in to stable end
product.
 Why this is important? • Return the organic matter to field ; reduce depletion
of resources • Arrest OM ; Reduce to pollute D/S of resource flow

Biological Principle
 General Nutritional requirement of microorganism
 Type of microbial metabolism
 Types of microorganism
 Environmental requirements
 Aerobic and anaerobic transformation
 Process selection

 Nutrient requirement of microbial growth
 To continue reproduce and function properly an organism must have a source
of energy, and inorganic elements as nutrient 1. Source of energy 2. Nutrient
and growth factors carbon and energy sources usually called substrates
 NPKS Ca Mg Fe Na Cl are major nutrients Zn, Mn, molydebenum Mo,
selenium Se, cobalt, copper, nickel etc are minor nutrient
 Growth factors are compound as constituent of organic cell material amino
acid, purines, pyrimidines, vitamins

Classification of Microorganism
 Depending upon the use of energy sources and carbon the classification of
microorganism
 Autotrophs carbon derived from CO2
 Heterotrophs carbon from organic
 Use light energy sources called Phototrophs
 Use energy from chemical reaction chemotrophs

 Microbial nutrition and biological conversion processes
 The main objective of BCP
 Conversion of OM in the waste into a stable end product
 Chemoheterotrophic organism are primary importance
 In SW adequate amount of nutrients are available to support the biological
conversion of the waste ( if needed addition is necessary especially in
industrial waste)

Types of Microbial Metabolism
 Metabolism is the process (all the chemical process that occurs in a living
organism as their metabolic type and their requirement of molecular oxygen
 Obligate aerobic- aerobic respiration (accept molecular oxygen ) respiratory
metabolism
 Fermentative metabolism ; does not involve the participation of an external
electron acceptor (obligate anaerobic) absence of oxygen
 Anoxic ; oxidised inorganic compound function as electron acceptor for some
respiratory organism in the absence of molecular oxygen eg nitrate and
sulphate
 Facultative anaerobic; can grow in either /or absence of molecular oxygen
 True facultative (depends on oxygen
 Aero-tolerant anaerobic ( insensitive to the oxygen)

Types of Microorganism
 Microorganism are commonly classified on the basis of cell structure as;
 Eucaryotes
 Eubacteria
 Archaebacteria
 Eubacteria & Archaebacteria are primary importance in biological conversion
of the organic fraction of SW and generally referred as bacteri

Environmental Requirement
 For biological conversion a favorable environment is necessary;
 Temperature and pH are important environmental parameter for survival and
growth of microorganism
 The growth of microorganism is optimum in narrow range
 The survival is possible in boarder range
 If temperature increase 10 deg c growth will be double until the optimum
temperature

Environmental Requirement
 pH range 6.5 to 7.5
 Moisture content: For optimum growth of bacteria moisture is necessary 50
to 60 %
 Free from Any types of heavy metal concentration, ammonia, sulfides and
other toxic constituent

Aerobic biological Transformation
 The general aerobic transformation of solids waste can be explain by following
decomposition equation
 Organic matter + O2 +nutrients -----new cells+ resistant organic matter
+CO2 +H2 O +NH3 +SO42- + ….+heat
 Organic matters are;
 Proteins, amino acid, lipids, carbohydrates, cellulose, lignin

Anaerobic biological transformation
 OM+H2O +nutrients-------- new cells + resistant organic
matter+CO2+CH4+NH3+H2S+heat

Biological process selection
 Aerobic simple
 Anaerobic energy benefit
 Characteristics Aerobic process Anaerobic process
 Energy use Net energy consumer Net energy production
 End products Humus, co2, H2O Sludge CO2, CH4
 Volume reduction Up to 50% Up to 50 %
 Processing time 20 to 30 days 20 to 40 days
 Primary goal Volume reduction Energy production
 Secondary goal Compost production waste stabilization

Composting (Aerobic)
 Commonly used biological process
 Applied for yard waste, separated MSW, commingled MSW co composting with
waste water sludge
 “Composting is the biological decomposition of biodegradable solid waste under
controlled predominantly aerobic conditions to a state that is sufficiently stable for
nuisance-free storage and handling and is satisfactorily matured for safe use in
agriculture”. ( General definition)
 “Composting is a decomposition process in which the substrate is progressively
broken down by a succession of populations of living organisms. The breakdown
products of one population serve as the substrate for the succeeding population.
The succession is initiated by way of the breakdown of the complex molecules in the
raw substrate to simpler forms by microbes indigenous to the substrate”. (ecological
definition)
 The process steps includes
 Preprocessing of MSW
 Aerobic decomposition
 Product preparation marketing

Composting Technologies
 windrow
 aerated static pile
 in-vessel composting and anaerobic processing (EPA, 1989 and 1995)
 They vary in the method of air supply, temperature control, mixing/turning of
the material, time required for composting, and capital and operating costs.
Besides these general categories of composting technologies, there are also
some supporting technologies, which include sorting, screening, and curing

 Quality of compost depends on •Composition of input material •Condition
available for composting •Extent of decomposition
 Particle size and particle size distribution 25 to 75mm
 Seeding and mixing requirements 1:5 partial decompose SW
 Mixing and turning of compost Total oxygen requirement Moisture content
Temperature and temperature control To prevent caking, drying, channeling
50 % initial oxygen 50 to 60 % 50 to 55 deg c
 Carbon/ nitrogen ratio 25 to 50 by mass
 pH 7 to 7.5
 Degree of decomposition Respiratory quotient Control of pathogen
 Area (land) requirement 50 ton/d 1.5 to 2 acre

Biochemical Reaction Phase

Biological Succession

 Nutrient balance
 C/N ratio is most important
 P important
 S, Ca trace element Less imortant
 C/N ratio 20 to 40
 better result 25 to 30

 Method of composting
 Windrow composting
 Static pile
 Forced air aeration
 In vessel composting
 Plug flow
 Continuous
 Community and home composting
 Bin composting

Temperature and pH ranges in Composting

Composting Process Application
 Yard waste collected separately
 Organic fraction of MSW
 Partially processed commingled MSW
 Co composting Waste water treatment plant sludge with organic fraction of
MSW
 Commercial composting system

Issues in the Implementation of Composting Facilities
 Production of odor
 Presence of pathogens( public health issues)
 Presence of heavy metal
 Desired material for quality compost
 facility of sitting
 Proper process design and operation
 Biological odor management
 Public health issues
 Heavy metal toxicity
 blowing of paper and plastic especially in windrow

Major Cause of Odor
 Low C/N ratio
 Environment
 Poor temperature control
 Excessive moisture
 Poor mixing of waste

Vermicomposting
 Vermiculture or vermicomposting is derived from the Latin term vermis,
meaning worms.
 Vermicomposting is essentially the consumption of organic material by
earthworms. This speeds up the process of decomposition and provides a
nutrient-rich end product, called vermicompost, in the form of ‘worm
castings’.

Vermicomposting
 Why vermicompost?
 keep valuable resources out of the landfill
 grow better veggies
 having fun looking at tiny critters in the worm bin
 feeling good at recycling nutrients that don't need to be wasted
 making a few bucks now and then, selling worms to new composters

Vermicomposting
 Two species of red earthworms have consistently been used for commercial
composting or worm farming, due to their relatively high tolerance of
environmental variations:
 Eisenia foetida-- The Red Wiggler;
 Lumbricus rebellus --The Red Worm.

Continuous Flow System
 The continuous flow system was developed by Dr. Clive Edwards at the
Rothamstead Agricultural Research Station.
 These systems are quickly gaining popularity and have been adopted by many
mid-scale operations.
 The efficiency savings offered by their continuous flow design increases with
the amount of material processed.

Vermicomposting

Vermicomposting
 The bedding for vermicomposting systems must be able to retain both
moisture and air while providing a place for the worms to live. Bedding does
not have to be purchased and most of us have plenty of bedding resources in
our home, office or school. Here are some suitable sources of bedding.
 Shredded corrugated cardboard is an excellent bedding, but is difficult to
find.

Vermicomposting
 Shredded paper like newspaper and computer paper is easy to find, but may
dry out quicker than corrugated cardboard. There is not a problem with the
ink from the paper.
 Peat moss has a low pH level that may cause a problem for the worms and it
is more expensive.
 Commercial worm bedding is available in sporting goods stores, but it is also
more expensive.

Vermicomposting
 The amount of bedding you need depends on the size of the box.
 A 2' x 2' box will need between 4 and 6 pounds of dry bedding, a 2' x 3' box
will take 9–14 pounds.
 No matter what the size, the bin should be 2/3 filled with “fluffed,” prepared
bedding
 For smaller bins, experiment — prepare excess bedding, it can be dried,
stored and used another time

Thermal Conversion of Solid Waste
Thermal conversion of solid waste can be defined as the conversion of solid
waste into gaseous, liquid and solid conversion products with the concurrent or
subsequent release of heat energy.

Incineration
 Incineration simply means reducing something to ashes by means of
combustion.
 Solid waste are reduced to ashes by means of combustion.
 In other words, Incineration is a chemical reaction in which carbon, hydrogen
and other elements in the waste mix with oxygen in the combustion zone and
generates heat.

Incineration
 It reduces the volume 85 % to 95 %.
 The end products are CO2, H2O, N2 and small amount of SO2 and ash.
Depending upon the amount of air supplied to the incinator , there are mainly
three types of combustion process.

Type of Incinators
1. Combustion : Stoichiometric or Excess air (includes Mass fired , RDF fired and
Fluidized bed)
2. Gasification : Partial combustion in sub stoichiometric condition
3. Pyrolysis : Absence of air

Stoichiometric Combustion
 Combustions with exactly the amount of oxygen needed for complete
combustion is known as stoichiometric combustion.

Excess Air Combustion
Due to inconsistent nature of solid waste ,it is virtually impossible to combust
solid waste with stoichiometric amounts of air. In practical combustion systems,
excess air must be used to promote mixing and turbulence, thus ensuring that air
can reach all parts of the waste. Increase in amount of air thus the amount of
oxygen decreases the combustion temperature. Thus air can be used to control
the combustion temperature.

Determination Of Effect Of Excess Air In Temperature And
Composition Of Flue Gases

Material And Heat Balance For The Combustion Of Solid
Waste

Mass Fired Combustion System
 Un-separated commingled waste is charge .
 External energy like diesel may be required to fire the waste.
 Where heat content is very low additional energy may be required for
combustion.
 Moisture content of MSW is important as it diminishes gross calorific value of
the waste.

Modern Mass Fired Combustor

RDF Fired Combustion System
 RDF stands for Refuse Derived Fuel.
 MSW prepared for combustions in the form like shredded ,pellet ,cubes.
 Comparatively smaller size of incinerator is required.
 Combustion is more controlled compred to Mass Fired system due to more
homogeneous nature of RDF.
 Advantages : Fair consistency in energy content, High efficiency in combustion.

Modern RDF Fired Combustor with travelling Grate Stroker

Fluidized Bed Combustion
 Fluidized bed combustion (FBC) is a combustion technology used to burn solid
fuels.
 In its most basic form, fuel particles are suspended in a hot, bubbling fluidity
bed of ash and other particulate materials (sand, limestone etc.) through
which jets of air are blown to provide the oxygen required for combustion.

Fluidized Bed Combustion System for RDF

Heat Recovery System
 Energy can be recovered from the hot flue gases generated by the combusting
MSW or RDF.
 Obtained hot water can be used as space-heating application.
 Where as Steam can be used as both heating and electricity generation .
 Waterwall Combustion Chamber and Waste Heat Boiler are two methods used
in Heat Recovery System.

Waterwall Combustion Chamber
 Wall of combustion chamber are lined with numbers of boiler tube.
 Water is circulated through the tubes .
 Tubes absorbs heat generated from combustion and produces steam.
 Usually the furnace wall areas adjacent to the grates are lined with refractory
(heat-resistant) material to protect tube from excessive temperature and
mechanical abrasion.

Section Through a Waterwall Heat Recovery Method

Waste Heat Boiler
 Wall of combustion chamber is lined with insulating material to reduce heat
loss through wall.
 All the hot flue gases are passed through a separate waste heat boiler located
externally to the combustion chamber .
 It also produces steam same as waterwall combustion chamber method .

Flow Diagram Of Waste Heat Boiler

Glasification
The process involves partial combustion of carbonaceous fuel to generate a
combustible gas reach in carbon monoxide hydrogen and some saturated
hydrocarbons principally methane.

Types of Glasifiers
1. Horizontal fixed bed : produces low-BTU gas and when heat recovery system
is added the steam or hot water obtained can be used for heating
application.
2. Vertical fixed bed : produces low-BTU gas and char.
3. Fluidized bed : produces medium-BTU gas.

Schematic Diagram of Batch Fed Vertical Fixed Glasifier

Pyrolysis
 Is destructive distillation or combustion in absence of air.
 It uses an external source of heat to drive the endothermic pyrolysis reaction
in an oxygen free environment.
 The end products of pyrolysis consist of char,pyrolytic oil and gases.
 Pyrolysis reaction for cellulose

Occidential Flash Pyrolysis System for Organic Part of MSW

Problems In Operation Of Pyrolysis System
 Failure of the front-end system to meet purity specification for alumunium
and glass , which affected the economics of the system.
 Failure of the system to produce a saleable pyrolysis oil . The oil produced had
a moisture content of 52%,not the 14% predicted from the pilot plant results.
The increased moisture in the oil decreased the energy content to 3600 Btu/lb
, as compared to the 9100 Btu/lb predicted by the pilot plant tests.

Environmental Consideration
Causes of environmental impact:
 Gaseous and particulate emission(CO,NO , SO2,NO2)
 Solid residues
 Liquid effluent
 Dioxins and Furans

Air Pollution Control
Gaseous and particulate air emissions control:
 Electrostatic precipitators, fabric filters, electrostatic gravel bed filters
(particulate control).
 Source separation, combustion controls, flue gas treatment (NO, control).
 Source separation, wet or dry scrubbing (SO and acid gas control).

Air Pollution Control
 Combustion controls (CO and HC control) .
 Source separation, combustion controls, particulate control (non-criteria
pollutant controls).

Electrostatic Precipitator

Fabric Filters

Wet Scrubbers

Dry Scrubbers-Spray Dryer

Dry-Scrubbers-Teller Dry Scrubbing System

Chapter----five---Resource Recovery.pptx

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