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Wednesday, June 02, 2010 Edit This 0 Comments »
Thermal treatment of waste if the combustion of MSW under controlled conditions, recovering renewable energy in the form of electricity and/or heat - EfW or WtE. This process includes incineration, gasification and pyrolysis.
CV for MSW is typiclly 9MJ/kg - Feed hopper, Flue Gas, Drying, Pyrolysis, Combustion, Burnout, Ash quench. Refuse Derived Fuel (RDF) / Waste Derived Fuel (WDF) is the high calorific fraction of processed MSW. Glass and metal don't have the calorific value.
There are 4 thermal processes:
- Gasification=some air
- Advance thermal treatment - incineration with energy recovery
- Pyrolysis=no air
- Incineration=excess of hair
Process of Incineration:
(i) organic substances converted to gases (C and H in waste converted to CO2 and H20)
(ii) Gas and particles burnt
Advantages:
- Can occur near to the site collection
- No CH4 is produced
- Source of energy
- Bottom ash residues can be re-used
- Large volume reduction
- Resulting in a biologically sterile ash product
Disadvantages:
- Higher costs compared to landfill
- Production of residue
- Perception of the emissions affecting the human health
- Perception of hungry burners
- Lack of flexibility - WMS must be functioning for many years, stable supply at least 100,000 t/yr, Lowest CV at least 7MJ/kg, long contracts in place-must be more than 15 years, hence high capital cost, planning and public opposition can be resolved
- Design to specific CV
Chemistry of combustion:
C20H32O10 + 02 -> CO2 + H20
Effective combustion:
- Temperature
- Residence Time
- Turbulence
- Excess of oxygen
Mass Burn Incineration:
- Lots of oxygen
- A degree of pre-sorting
- 25t/day up to more than 3000t/day
Recent development:
- Fluidised Bed Incinerators - fuel sand particles are combusted in the furnace while getting suspended in a stream of hot gas. Gases and bed material mixed to ensure complete combustion. Can be used to incinerate liquids, sludges, solids and gases.
- Legislation - get the permit from IPPC, control emissions by ECWID, UK WIR, Ash disposal according to Landfill Directive
Advantages of fluidised bed:
- High combustion efficiency
- Less ash
- Good emissions control
- Better combustion condition
- Residence time calculations are reliable
- Perception of being more environmentally responsible than mass burn incineration
Disadvantages of fluidised bed:
- Ash is still produced
- Requires pre-sorting
- Slower than a mass burn-unit
- Limited us in the UK
- High capital costs
- Negative public perception
- Dioxin emissions
- Minimum tonnage required
Okay, haha since i could not get my hands off the lappy, I think it's time to turn 'blogging' into something useful! This is the summary from one of the topics for my final paper later, in a bout 6 hours!
Love,
Fizzah
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