Thermal Methods Flashcards
What is thermal treatment of Waste?
Combustion of MSW under controlled conditions, recovering renewable energy in the form of electricity and/or heat.
What are the main methods of Thermal treatment of waste?
Incineration, Gasification & Pyrolysis.
What is Thermal Degradation?
The molecular deterioration of the materials because of over heating.
It occurs at a temperature at which some components of the material separate or react with one another or with the atmosphere to modify the macro or microstructure.
What is the difference between Incineration, Gasification and Pyrolysis?
1) Incineration - combustion in excess air
2) Gasification - Partial Oxidation
3) Pyrolysis - Combustion in the absence of air
What is the objective of thermal technology?
1) To reduce volume and Weight
2) Recover conversion products and energy
Why is Pollution Control Necessary?
Because of:
1) Dioxins and furans
2) Heavy Metals
3) Toxic and corrosive gases
4) Polycyclic aromatic hydrocarbons (PAHs)
5) Wastewater / fly ash / bottom ash
Why is the Calorific value Important?
1) The higher the calorific value the more energy is produced
2) There is a minimum value plants use - 9MJ/kg
Briefly explain the Incineration Process?
- Converts all C and H to C02 and H20
- Two stage process
1) Organic substances turned into gases ( <30 mins)
2) Gas and particles burnt ( 2-3 seconds)
Advantages of Incineration (+)
1) Can occur near point of collection
2) Result is a biologically sterile ash product
3) Large volume reduction
4) Produces no methane
5) Sources of energy
6) Reusable bottom ash residues
7) Best Practical Environmental Option for certain hazardous wastes
Disadvantages of incineration (-)
1) Higher costs and high capital investment compared to landfill.
2) Perception of hungry Burner - to stay efficient - restricting other waste options
3) Lack flexibility
4) Specific Calorific Value design of system
5) Perception that emissions adversely affect health
6) Production of residue
What does the application Incineration Require?
1) Well functioning waste management system
2) stable supply - 100,000 tonnes/year
3) Lowest CV at least &MJ/kg
4) Long contracts in place
5) Planning and public opposition resolved.
Controlling factors of combustion
1) Sufficient Temperature
2) Sufficient Residence Time at temperature
3) Turbulence
Plus an excess of oxygen
What is a fluidised bed incinerator?
A type of furnace where the fuel particles are combusted while suspended in a stream of hot gas.
Bed consists of sand particles
Gases and bed continuously mix to ensure complete combustion
Can be used to incinerate liquids, sludges, solids or gases.
What are the Advantages of a Fluidised bed (+)?
1) Perception of being more environmentally responsible
2) High combustion efficiency
3) Residence time calculations are reliable
4) good emissions control
5) Less ash
6) Relatively low Maintenance - no moving parts
7) Better combustion conditions - sand provides continuos attrition of burning material and exposes fresh material for combustion
Disadvantages of a fluidised bed (-) ?
1) requires treatment of waste
2) Lower throughputs - 35% less
3) Limited commercial use UK
4) High capital costs
5) dioxin emissions
6) Minimum tonnage - hungry
7) ash produced - but less
8) negative perception of incinerators in general
