21 – Landfill gas
21 Landfill gas
21 – Landfill gas
21 Landfill gas
Overview
21.1 Landfil gas production
21.2 Prognosis of landfill gas production
21.3 Extraction systems
21.4 Production monitoring
21 – Landfill gas
21.1 LFG production
Waste contains a certain amount of degradable organic
matter
Microbiological processes result in the formation of
landfill gas (LFG)
21.1 – Landfill gas
21 – Landfill gas
21.1 Landfill gas production
Degradation follows 4 biological stages during waste
disposal:
1.
Hydrolosis
2.
Acidogenesis
3.
Acetogenesis
4.
Methanogenesis
21 – Landfill gas
Biological processes
21 – Landfill gas
Hydrolosis
In the first stage complex solid organic material is
solubilized by enzymes excreted by hydrolytic
micro-organisms
21 – Landfill gas
Acidogenesis
In the second stage soluble organic components
including the products of hydrolysis are converted
into organic acids and alcohols
21 – Landfill gas
Acetogenesis
In the third stage the products of acidogenesis
are converted into acetic acid, hydrogen and carbon
dioxide
21 – Landfill gas
Methanogenesis
In the fourth and final stage methane is formed
mainly from acetic acid or from hydrogen and
carbon dioxide. Methane can also be formed
directly from products of the acidogenesis such as
formic acid and methanol
21 – Landfill gas
Composition
LFG primarily consists out of methane (CH
4) and
carbondioxide (CO
2)
Ratio CH
4:CO
2= 50:50 (theoretically)
CH
3COOH (Acetic acid) --> CH
4+ CO
2
CO
2is more soluble in water, ratio shifts to
60:40
21 – Landfill gas
Composition (cont’d)
CH
4is a green house gas (GHG) with a GHG potential of
21 times that of CO
2
1 ton of CH
4has an equivalent of 21 ton of CO
2
LFG can contain traces of hydrocarbons, halogenated
hydrocarbons and sulphur compounds
21 – Landfill gas
21.2 Prognosis of LFG production
Modelling with LFG production models
Only two models are validated
First order model
Multi phase first order model
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First order model
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First order model – organic content
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Multi phase first order
21 – Landfill gas
Multi phase first order – organic content
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Organic matter and Organic C
21 – Landfill gas
Prognosis of LFG production
21 – Landfill gas
Prognosis of LFG production
Only two models are validated Uncertainty depending on:
1. Waste composition
2. Degree of pre-treatment
3. Type and degree of compaction, method of operation, type and
thickness of cover material
4. Quantity of refuse, geometry and hydrogeolocic properties of landfill
21 – Landfill gas
21.3 Extraction systems
Lay out of an extraction system
Various types of extraction systems
Recovery efficiency
21 – Landfill gas
Lay out
emission
oxidation
extraction
21 – Landfill gas
Various types of extraction systems
1.
Vertical
2.
Horizontal
3.
Slope
4.
Point
21 – Landfill gas
Vertical
Conventional Cell wise
Build up GRAVEL Build up + early extraction HDPE piping (non
-perforated)
21 – Landfill gas
Horizontal
21 – Landfill gas
Slope
21 – Landfill gas
Point
21 – Landfill gas
Gas well connection
RULE OF THUMB: 4 GAS WELLS PER HA
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Gas well connection
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Recovery efficiency
21 – Landfill gas
21.4
Production monitoring
Monitoring equipment
Anemo meter Digital mano meter
Gas analyser
21 – Landfill gas
Gas analyser can measure:
1.
CH
42.
CO
23.
O
24.
N
2(= 100% - CH
4% - CO
2% - O
2%)
21 – Landfill gas
If CH4 and O2 concentration respectively in a gas
well is:
> 50% and < 1% then
more extraction
< 50% and > 1% then
less extraction
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If N
2:O
2ratio is:
> 5
indicator suction of ambient air
< 4
indicator leakage piping extraction system
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21.5 Flaring, electricity and heat production
A suitable nearby use for LFG must be identified
The landfill must have a depth of at least 5 m. and preferably
10 m. of unsaturated biodegradable waste
Amount of waste deposited: 0.5 Million tonnes
Waste should not be too old (between 5 – 10 years, less if
mainly food and vegetable wastes)
Leachate level should be at least 5 m. below the landfill
surface
21 – Landfill gas
Flaring
Open flare
Enclosed flares
Passive flare
21 – Landfill gas
Heat production
LFG fired boilers
Heat exchangers WWTP
21 – Landfill gas
Electricity production
