From waste - to - energy

Some fundamental physico-chemical background information

Does it make you think of...?

Or rather of...?

Waste...

The waste problemFrom waste to energy, basic principles

Content

The waste problem

- What is waste?

- How much waste is produced?

- Why is waste a problem?

- What can we do to solve that

problem?

- Why not just dump it?

Content

What is waste?

• Technical: a product not longer wanted by its producerNote: it can still be a valuable raw material to others!

• Economical: a product for which one has to pay to dispose of

• Legal: “each matter or object of which the owner wants , plans or has to dispose of”

• Different categorisations are possible: according to origin, composition etc.

organic48%

paper and cardboard

17%

glass3%

metals4%

plastics8%

mixed9%

textiles2%

inerts4%

remainder5%

Typical waste composition

Inerts25%

Water 25%

Combustible50%

Oxygen41%

Hydrogen7%

Carbon51%

Nitrogen1%

Remainder0,2%

Composition

Heterogeneous in nature: varies widely according to

– Season, time of the year

– Weekday / weekend

– Life style

– City / countryside

– Collection method

– Sorting of recyclablematerials (source separation)

Waste production in Flanders

Waste characterisation

C, H

LHV = Lower Heating Value

Moisture, O2

42001000

126003000

168004000

84002000

Asia

EuropeEurope

kJ/kgkcal/kg

USARDF

Variation and changes in waste composition

– Household waste: approx. 1 kg /p/day

– industrial waste eq. to household waste

– market waste

– street cleaning waste

– residual waste of sorting centres

– bulky waste

Total: between 0.5 and 2 kg per capita per dag

Waste production in Flanders

How much waste is produced?

• Avoid waste

• Reduce, e.g. through re-use

• Selective collection in separate fractions:– Organic waste (garden, fruit and vegetable waste) for

composting

– Paper, glass for recycling

– Plastics, for re-use in other applications

• Thermal valorisation with energy recovery

• Other?

How can we reduce the waste mountain?

No,

there always remains a non-recyclable fraction

• mixed too much, making separation not feasible

• recuperation economically not interesting

• recycling technically not possible

Long term goal: 150 kg per person per year

Change of mentality

Will we ever be able to completely avoid waste?

• Soil pollution (leaching out of toxic substances,...)

• Odour and dust nuisance

• Visual pollution

• Loss of valuable ground

• Postponing problems to next generations

• Uncontrolled release of hothouse gases

• Vermin

• Loss of energy:

““dumping 3 tons of waste = dumping 3 tons of waste = burying 1 ton of coal!”burying 1 ton of coal!”

““dumping 3 tons of waste = dumping 3 tons of waste = burying 1 ton of coal!”burying 1 ton of coal!”

Why is dumping to be avoided?

The waste problem From waste to energy, basic principles

Physico-chemical principlesWhat is combustion?How much energy can we make from waste?What can we do with this energy?

Content

Combustion = oxidisation = reaction with oxygen

1. Combustible parts react with oxygen from the air

C + O2 -> CO2 (carbon dioxide) + heat (33 MJ/kg)

H + O2 - > H2O (water vapour) + heat (121 MJ/kg)

2. The water evaporates

3. Inert materials are not modified

What happens when waste ‘burns’?

DryingDegassing

Pyrolysis

Fixed carbon oxidation

Burn-out and slag cooling

Gas combustion

Gas post-combustion (850°C/2s)

Combustion is not one single physico-chemical process but a series of different consecutive processes.

What are the different combustion phases?

4.5 Nm³ air

1 kgwaste

5.2 Nm³ flue gases

250g inert ashes

FURNACE

heat

Volume reduction15:1

How is waste transformed?

1 kg waste = average 10 megajoule (MJ) (range: 7.5

- 15 MJ)

Compare this with:1 kg fuel = 42 MJ1 kg carbon = 30 MJ1 kg dry wood = 15 MJ1 kg dry peat = 12 MJ

By the way…

with 10 MJ of energy one can heat 80 liters of water by

30°C, so... 1 kg waste = 1 hot shower !

How much heat is released?

75 W

Make hot water, e.g.– for heating purposes (district heating, hot houses)

Make steam e.g.– for industrial applications– to make electricity– for a combination of both (co-generation)

What can we do with this heat?

1 kg waste = 0,675 kWh

i.e., with 1 kg of waste this light bulb can burn 9 hours

75 W

How much electricity can be made?

© Keppel Seghers Group of Companies, 2005 - MStore_3P_en_003_B