Incineration Flashcards
what does the IED aim
Protect health and environment
Application of BAT
Requires a permit to ensure compliance
Public participation in decision making
What are some advantages of incineration? 4
Can be carried out close to waste collection
Reduced to a biologically sterile ash
Can be used as source of energy
Valorisation of bottom ash
Disadvantages of incineration. 5
High capital and operational costs with long payback periods
Long term contracts required which reduces flexibility
Designed on a certain CV, removal of plastic and paper may affect performance
Public concern on health
Still produces solid residue that requires management
Why is there a range in emission limit values
Depends on the content of pollutant in the waste.
How does ash and moisture and volatiles in waste affect performance
Ash/moisture - reduces CV of the waste
High volatiles (plastics) increase CV and can cause thermal overload
BAT for NOx, SOx, particulates, metals and HC
NOx - SCR
SOx - wet scrubber
Particulates - ESP
Metals - fabric filter/ESP
HC - fabric filter
What is CV of MSW?
What contributes the highest and lowest
9MJ/kg
Highest - plastics
lowest - metals
How to make money from incineration?
Selling energy (20%)
Gate fee (80%)
Implications for overfeeding high CV waste
Thermal overload which impacts thermal integrity and breakdown. Max a few hours
Implications for overfeeding low CV waste
Causes incomplete burnout of waste (legal requirement for <3% carbon in ash)
What is the legal requirement for carbon in ash?
3%
How is the CV of the waste homogenised
Prior to incineration by the crane operator.
Steps in incineration system
1.) Bunker and feeding
2.) Furnace and combustion chamber
3.) Boiler > heating or electricity
4.) Treatments
What happens in the bunker
holds 2-3 days of waste. Crane mixes the waste and removes dangerous items. Fed by a steel hopper
How is air provided in the furnace
1.) primary air blown evenly on the underside of the grate. Secondary air through nozzles above to ensure excess air and turbulence.
Steps in the furnace
1.) Moisture driven off in Lower temperatures
2.) Waste undergoes thermal decomposition and pyrolysis or organic material -> VM and gas
3.) Devolatilisation 500C
4.) Combustion of volatiles at 1000C
What is the role of grates in the furnace
Ash and metal residue discharged continuously at the end of grate where it is quenched
Automatic and move to discharge providing agitation and tumbling
How is the process measured and controlled
Measure oxygen content, steam production and gas temperature
Control - waste feed speed
Grate speed
Combustion air flow and distribution
Benefits of energy recovery (3)
20% of income comes from power and heat
On site use of power and steam
EU legislation
How is the combustion gases cooled for heat recovery
By a boiler to produce superheated steam (450C).
Steam drum>superheated?steam>hot water
Afterwards there may be an economiser to produce hot water
What are some conditions in the flue gas?
Very high temperatures, variating due to the heterogeneous fuel
High dust - fouling and erosion
Corrosive
What causes fouling? implication
How to stop fouling
Dust load and flue gas velocity
Increases with fly ash, SO3 and HCL
Reduces heat transfer
Soot blowers, explosion or sonic horn
What causes boiler tube corrosion.
How to protect?
Low T - dew point high moisture creates acid gas, SO3, HCl
High T - reduced MPt, mixture of steel, flyash, SO3 and HCL
Ceramic
What causes a higher corrosion for a set tube wall temperature
Increased flue gas temperature
How is energy utilised in incineration?
Electricity, district heat, CHP
How is electricity, heat and CHP generated.
Electricity - steam turbine
Heat - Steam HX
CHP - Different type of steam turbine with effluent used for heat
How much energy is lost in generating electricity
60%
How does a CHP differ to electricity generation
Some steam is extracted at 140C for useful heat
Barriers to CHP (2)
High capital costs and requires backup boiler
Must have an anchor load to ensure long term contracts (hospitals)
How is bottom ash used? Fly ash?
secondary aggregate or landfill
Hazardous landfill
How is ash removed in APC
bag filter, ESP
What is the composition of bottom ash?
Bulk of total as and heterogeneous mix of slag, metals, glass and incombustible material.
Metals can be recycled, unusable landfilled. Can be used as an aggregate.
How is bottom ash treated for aggregate products
1.) stored for 2 weeks to assess hazards
sieving screening
Treatment of flyash
High content of heavy metals, dioxins or furans
Landfilled (expensive)
Vitrification
Carbonation
Vitrification
High temperature melting to produce a slag and recyled as a building product
Carbonation
CO2 reactions with calcium ions in APC to form calcium carbonate, reducing pH and leachability
Secondary aggregate for building industry
Features of fluidised bed incinerators
MSW needs pre-screening and shredding
Rapid continuous mixing of solids to create isothermal conditions
High heat transfer rates - fast ignition and combustion
Lower combustion T - lower NOx
