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