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Bioenergy > Incineration > Flashcards

Incineration Flashcards

1
Q

what does the IED aim

A

Protect health and environment
Application of BAT
Requires a permit to ensure compliance
Public participation in decision making

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2
Q

What are some advantages of incineration? 4

A

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

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3
Q

Disadvantages of incineration. 5

A

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

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4
Q

Why is there a range in emission limit values

A

Depends on the content of pollutant in the waste.

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5
Q

How does ash and moisture and volatiles in waste affect performance

A

Ash/moisture - reduces CV of the waste
High volatiles (plastics) increase CV and can cause thermal overload

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6
Q

BAT for NOx, SOx, particulates, metals and HC

A

NOx - SCR
SOx - wet scrubber
Particulates - ESP
Metals - fabric filter/ESP
HC - fabric filter

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7
Q

What is CV of MSW?
What contributes the highest and lowest

A

9MJ/kg
Highest - plastics
lowest - metals

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8
Q

How to make money from incineration?

A

Selling energy (20%)
Gate fee (80%)

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9
Q

Implications for overfeeding high CV waste

A

Thermal overload which impacts thermal integrity and breakdown. Max a few hours

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10
Q

Implications for overfeeding low CV waste

A

Causes incomplete burnout of waste (legal requirement for <3% carbon in ash)

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11
Q

What is the legal requirement for carbon in ash?

A

3%

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12
Q

How is the CV of the waste homogenised

A

Prior to incineration by the crane operator.

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13
Q

Steps in incineration system

A

1.) Bunker and feeding
2.) Furnace and combustion chamber
3.) Boiler > heating or electricity
4.) Treatments

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14
Q

What happens in the bunker

A

holds 2-3 days of waste. Crane mixes the waste and removes dangerous items. Fed by a steel hopper

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15
Q

How is air provided in the furnace

A

1.) primary air blown evenly on the underside of the grate. Secondary air through nozzles above to ensure excess air and turbulence.

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16
Q

Steps in the furnace

A

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

17
Q

What is the role of grates in the furnace

A

Ash and metal residue discharged continuously at the end of grate where it is quenched

Automatic and move to discharge providing agitation and tumbling

18
Q

How is the process measured and controlled

A

Measure oxygen content, steam production and gas temperature

Control - waste feed speed
Grate speed
Combustion air flow and distribution

19
Q

Benefits of energy recovery (3)

A

20% of income comes from power and heat
On site use of power and steam
EU legislation

20
Q

How is the combustion gases cooled for heat recovery

A

By a boiler to produce superheated steam (450C).
Steam drum>superheated?steam>hot water

Afterwards there may be an economiser to produce hot water

21
Q

What are some conditions in the flue gas?

A

Very high temperatures, variating due to the heterogeneous fuel

High dust - fouling and erosion
Corrosive

22
Q

What causes fouling? implication
How to stop fouling

A

Dust load and flue gas velocity

Increases with fly ash, SO3 and HCL
Reduces heat transfer

Soot blowers, explosion or sonic horn

23
Q

What causes boiler tube corrosion.
How to protect?

A

Low T - dew point high moisture creates acid gas, SO3, HCl
High T - reduced MPt, mixture of steel, flyash, SO3 and HCL

Ceramic

24
Q

What causes a higher corrosion for a set tube wall temperature

A

Increased flue gas temperature

25
Q

How is energy utilised in incineration?

A

Electricity, district heat, CHP

26
Q

How is electricity, heat and CHP generated.

A

Electricity - steam turbine
Heat - Steam HX
CHP - Different type of steam turbine with effluent used for heat

27
Q

How much energy is lost in generating electricity

A

60%

28
Q

How does a CHP differ to electricity generation

A

Some steam is extracted at 140C for useful heat

29
Q

Barriers to CHP (2)

A

High capital costs and requires backup boiler
Must have an anchor load to ensure long term contracts (hospitals)

30
Q

How is bottom ash used? Fly ash?

A

secondary aggregate or landfill
Hazardous landfill

31
Q

How is ash removed in APC

A

bag filter, ESP

32
Q

What is the composition of bottom ash?

A

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.

33
Q

How is bottom ash treated for aggregate products

A

1.) stored for 2 weeks to assess hazards
sieving screening

34
Q

Treatment of flyash

A

High content of heavy metals, dioxins or furans
Landfilled (expensive)
Vitrification
Carbonation

35
Q

Vitrification

A

High temperature melting to produce a slag and recyled as a building product

36
Q

Carbonation

A

CO2 reactions with calcium ions in APC to form calcium carbonate, reducing pH and leachability
Secondary aggregate for building industry

37
Q

Features of fluidised bed incinerators

A

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

Bioenergy (7 decks)

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