optimising_anaerobic_digestion.pdf

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Optimising anaerobic digestion
Optimising anaerobic
digestion
digestion
Charles Banks
University of Southampton
Evaluating the Potential for Anaerobic Digestion to provide
Energy and Soil amendment
University of Reading
25th March 2009
Optimising anaerobic
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Digestion is an energy producing
process
process
• Up to 75% conversion of
substrate into biogas
• Biogas has a methane content
of 50-60% (but depends on
substrate)
• Biogas typically has a thermal
value of about 22 MJ m -3
Digestion is an energy producing
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Energy equivalents
• 1 Watt = 1 joule second -1
• 1 Wh = 1 x 3600 joules (J)
• 1 kWh = 3600000 J
• 1 kWh = 3.6 MJ
• 22 MJ (1m 3 biogas) = 22/3.6 kWh
• = 6.1 kWh
• Electrical conversion efficiency = 35%
Therefore 1m 3 biogas = 2.14 kWh (elec)
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So how much
energy do I get
energy do I get
from my digester?
from my digester?
So how much
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First we need to predict or measure
the methane content
the methane content
• First attempt to estimate this theoretically by
Buswell (1952), who devised a formula based
on chemical composition to predict theoretical
yields of component products from digestion
C c
H h
O o
N n
S s
+ 1/4(4c -
h -
2o +3n + 2s)H 2
O →
1/8(4c -
h + 2o +3n + 2s)CO 2
+ 1/8(4c + h -
2o
-3n -
2s)CH 4
+ nNH 3
+ sH 2
S
First we need to predict or measure
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