MSW to Energy Using Thermal Conversion Process
Presented ByAlam, Md TanvirID: 2015311947
Introduction
What is MSW ?
Definition: Waste generally means “something unwanted”. A material is considered as waste until it is considered as beneficial again. Thus a solid material considered as solid waste in the eye of producer when it loses its worth to them and is discarded.
Municipal Solid Waste (MSW) is the waste col-lected by urban local body
Composition of MSW
Income Level
Organic (%)
Paper (%)
Plastic (%)
Glass (%) Metal (%) Other (%)
Low Income 64 5 8 3 3 17
Lower Middle Income
59 9 12 3 2 15
Upper Middle Income
54 14 11 5 3 13
High Income 28 31 11 7 6 17
Types of waste composition by income level
Source: Waste Composition, World Bank
Chemical Properties of Waste Ultimate analysis of municipal solid waste ( percent by weight in dry basis)
Component Carbon (C) Hydrogen (H)
Oxygen (O) Nitrogen (N)
Sulphur (S) Ash
Food waste 49.1 6.6 37.6 1.7 0.2 4.8Paper 43.4 5.8 44.3 0.3 0.2 6.1Newsprint 49.1 6.1 43.0 0.1 0.2 1.5Cardboard 44.0 5.9 44.6 0.3 0.2 5.0Rubber 77.8 10.4 - - 2.0 9.8Plastics 60.0 7.0 23.0 - - 10PVC 45.2 5.6 1.6 0.1 0.1 47.4Leather 42.0 5.3 22.8 6.0 1.0 22.9Textile 55.0 6.5 31.2 4.5 0.2 2.6Wood 50.5 6.0 42.4 0.2 0.1 0.8Source: Kaiser (1978)
Proximate analysis and calorific value of MSWCompo-nent
Proximate analysis, % of weight Calorific value, kJ/kgMoisture content
Volatiles Fixed Car-bon
Ash As col-lected
Dry Moisture/ash free
Paper 10.2 76.0 8.4 5.4 15,750 17,530 18,650Newsprint 6.0 81.1 11.5 1.4 18,550 19,720 20,000Food waste 78.3 17.1 3.6 1.0 4,170 19,230 20,230Meat waste 37.7 56.3 1.8 4.2 17,730 28,940 30,490Grass 75.2 18.6 4.5 1.7 4,760 19,250 20,610Green Logs 50.0 42.2 7.3 0.5 4,870 9,740 9,840Plants 54.0 35.6 8.1 2.3 8,560 18,580 19,590Rubber 1.2 84.0 5.0 9.8 25,590 26,230 29,180Leather 7.5 57.1 14.3 21.1 16,770 18,120 23,500PVC 0.2 86.9 10.9 2.0 22,590 22,640 23,160Source: Kaiser (1978)
Why Waste to Energy ?
MSW to Energy Conversion Processes
Energy Conversion Processes
Waste
MBT
Mechanical Treatment
ThermalConversion
BiologicalConversion
Gasification
Combustion
Pyrolysis/Thermolysis
Anaerobic Diges-tion
Liquefaction Indirect Lique-faction / Metha-
nation
Biogas
Oil
Bio-Alcohol
Low Quality Syngas
Flue Gas
Crushing, Com-pressing, Pelletiz-
ingPretreatment
Residues
LandfillRecycling
Residues
High Quality Syngas
Oil
Solid Fuel (RDF)
PowerGeneration
Further Pro-cessing
Chemical Product
CONCEPT PROCESS ENERGY CARRIER
Thermal Conversion Processes
PyrolysisPyrolysis/GasificationConventional GasificationPlasma Arc GasificationMass Burn (Incineration)
Pyrolysis
Can be defined as thermal decomposition of carbon based materials in an oxygen deficient atmosphere using heat to produce syngas
No air or oxygen is present and no direct burning take place Thermal decomposition take place at elevated temperature ( 400-900 °C)
Process Schematic, MSW to Energy via Pyrolysis
Conventional Gasification
A thermal process, which converts carbonaceous materials such as MSW into syngas using a limited quantity of air or oxygen.
Gasification conditions: 800-1600 °CSteam is injected into the conventional gasification reactor to
promote CO and H2 Production
Chemical ReactionsDehydration: Drying process occurs around 100 °C. Resulting steam mixed into gas flow Water gas reaction:Pyrolysis: Occurs at around 200-300 °C Volatiles are released and char is producedCombustion: Volatile products and some of the char react with oxygen to primarily
form carbon dioxide and small amounts of carbon monoxide Reaction: C+ O2 CO2Gasification: Char reacts with steam to produce carbon monoxide and hydrogen Reaction:Reversible gas phase: Water-gas shift reaction reaches equilibrium very fast at the temperatures
in a gasifier. This balances the concentrations of carbon monoxide, steam, carbon dioxide and hydrogen.
Process Schematic, MSW to Energy via Conventional Gasification
MSW Preprocess-ing
Conventional Gasifica-
tion Reac-tor
Ash/ Slag & Metals
Recyclables
Syngas
Syngas Cleanup
Byproducts such as sulfur & acid
gases
Air/O2
Power genera-tion: Electrical Energy+ Steam
Air Emis-sions
Electric-ity to Grid
Pyrolysis/Gasification
Pyrolysis/gasification is a variation of the pyrolysis process Another reactor is added whereby any carbon char or pyrolysis liquids produced
from the initial pyrolysis step are further gasified in a closed coupled reactor Air, oxygen or steam used for gasification reaction Temperature range: Pyrolysis zone: 400-900 °C Gasification zone: 700-1500 °C
Process Schematic, MSW to Energy via Pyrolysis/Gasification
MSW Preprocess-ing
Pyrolysis/ Gasifica-
tion Reac-tor
Ash/ Slag & Metals
Recyclables
Syngas
Syngas Cleanup
Byproducts such as sulfur & acid
gases
Air/O2
Air Emis-sions
Power genera-tion: Electrical Energy+ Steam
Electric-ity to Grid
Plasma Arc Gasification A high temperature pyrolysis process whereby carbon based materials are con-
verted into syngas Inorganic materials and minerals of the waste produce rocklike glass by product
called vitrified slag High temperature is created by an electric arc in a torch whereby a gas is con-
verted into plasma Operating temperature: 4000-7000 °C
Process Schematic, MSW to Energy via Plasma Arc Gasification
MSW Preprocess-ing
Plasma Arc Gasifica-
tion Reac-tor
Vitrified Slag & Metals
Recyclables
Syngas
Syngas Cleanup
Byproducts such as sulfur & acid
gases
Air/O2
Power genera-tion: Electrical Energy+ Steam
Electric-ity to Grid
Air Emis-sions
Mass Burn (Incineration)
A combustion process that uses an excess of oxygen or air to burn the waste
Operating temperature: 500-1200 °C High pressure steam produced in the fluid bed boiler
Process Schematic, MSW to Energy via Mass Burn (Incineration)
MSW Preprocess-ing Fluid Bed
Boiler
Ash & Metals
Recyclables
Gas Cleanup
Byproducts such as sulfur & acid
gases
Air/O2
Power genera-tion: Electrical Energy+ Steam
Electric-ity to Grid
Air Emis-sions
Advantages of Gasification Over Others
Gasification has several advantages over traditional combustion processes for MSW treatment It takes place in a low oxygen environment that limits the for-mation of dioxins and of large quantities of SOx and Nox
It requires just a fraction of the stoichiometric amount of oxygen necessary for combustion. As a result, the volume of process gas is low, requiring smaller and less expensive gas cleaning equipment.
Gasification generates a fuel gas that can be integrated with combined cycle turbines, reciprocating engines and, potentially, with fuel cells that convert fuel energy to electricity more efficiently than conventional steam boilers.
Limitations of Gasification
During gasification, tars, heavy metals, halogens and alkaline compounds are released within the product gas and can cause environmental and operational problems.
Tars are high molecular weight organic gases that ruin reforming catalysts, sulfur removal systems, ceramic filters and increase the occurrence of slag-ging in boilers and on other metal and refractory surfaces
Alkalis can increase agglomeration in fluidized beds that are used in some gasification systems and also can ruin gas turbines during combustion.
Halogens are corrosive and are a cause of acid rain if emitted to the environ-ment.
Main Types of Gaisifier
Updraft Fixed Bed Downdraft Fixed Bed Fluidized Bed Entrained Bed
Updraft Fixed Bed
One is oldest and simplest type of gasifier. The air comes in at the bot-tom and produced syn gas leaves from the top of the gasifier.
At the bottom combustion reaction occurs, above that reduction reac-tion occurs.
In the upper part of the gasifier heating and pyrolysis of the feedstock occurs
Tars and volatile produced during the reaction will leave along with the syn gas at the top of the gasifier
The major advantages of this type of gasifier is its simplicity, high charcoal burn out and internal heat exchange leading to low tempera-ture of exit gas and high equipment efficiency
Major drawbacks result from the possibility of "channelling" in the equipment, which can lead to oxygen break-through and dangerous, explosive situations
Downdraft Fixed Bed
In updraft gasifier there is a problem of tar entrainment in the product gas leaving stream
The produced gas is taken out from the bottom hence fuel and gas move in the same direction.
Main advantage of downdraft gasifier lies in the possibility of producing tar free gas for engine operation.
Main disadvantage is that downdraft gasifier cannot be operated with range of dif-ferent feedstocks
Other disadvantage is it gives lower efficiency
Fluidized Bed Both up and downdraught gasifiers is influenced by the morphological, physical
and chemical properties of the fuel. Problems commonly encountered are: lack of bunker flow, slagging and extreme pressure drop over the gasifier
Air is blown through a bed of solid particles at a sufficient velocity to keep these in a state of suspension.
The bed is originally externally heated and the feedstock is introduced as soon as a sufficiently high temperature is reached
The major advantages of fluidized bed gasifiers are easy control of temperature, which can be kept below the melting or fusion point of the ash and their ability to deal with fluffy and fine grained materials (sawdust etc.) without the need of pre-processing
Drawbacks of the fluidized bed gasifier lie in the rather high tar content of the product gas, the incomplete carbon burn-out, and poor response to load changes
Entrained Bed
In entrained-flow gasifiers, feedstock's and the oxidant (air or oxygen) and/or steam are fed co-currently to the gasifier
Entrained-flow gasifiers operate at high temperature and pressure and extremely turbulent flow which causes rapid feed conversion and al-lows high throughput.
Environmentally most benign; produced syngas consists of mainly H2, CO and carbon dioxide (CO2) with trace amount of other contaminant
High carbon conversion, but low cold gas efficiency
High level of sensible heat in product gas, heat recovery is required to improve efficiency
Slagging occurs
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