1/38 21 – Landfill gas 21 Landfill gas 1. 2/38 21 – Landfill gas “Landfill gas is an explosive...
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Transcript of 1/38 21 – Landfill gas 21 Landfill gas 1. 2/38 21 – Landfill gas “Landfill gas is an explosive...
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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
21.5 Flaring, electricity and heat production
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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
Biological processes
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21 – Landfill gas
21.1 Landfill gas production
Degradation follows 4 biological stages during waste
disposal:
1. Hydrolosis
2. Acidogenesis
3. Acetogenesis
4. Methanogenesis
21.1 – Landfill gas production
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21 – Landfill gas
Hydrolosis
In the first stage complex solid organic material is
solubilized by enzymes excreted by hydrolytic
micro-organisms
21.1 – Landfill gas production
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21 – Landfill gas
Acidogenesis
In the second stage soluble organic components
including the products of hydrolysis are converted
into organic acids and alcohols
21.1 – Landfill gas production
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21 – Landfill gas
Acetogenesis
In the third stage the products of acidogenesis
are converted into acetic acid, hydrogen and carbon
dioxide
21.1 – Landfill gas production
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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
21.1 – Landfill gas production
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21 – Landfill gas
Composition
LFG primarily consists out of methane (CH4) and
carbondioxide (CO2)
Ratio CH4:CO2 = 50:50 (theoretically)
CH3COOH (Acetic acid) --> CH4 + CO2
CO2 is more soluble in water, ratio shifts to 60:40
21.1 – Landfill gas production
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21 – Landfill gas
Composition (cont’d)
CH4 is a green house gas (GHG) with a GHG potential of
21 times that of CO2
1 ton of CH4 has an equivalent of 21 ton of CO2
LFG can contain traces of hydrocarbons, halogenated
hydrocarbons and sulphur compounds
21.1 – Landfill gas production
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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
21.2 – Prognosis of landfill gas production
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21 – Landfill gas
First order model
tkt ekAC 1
1087.1
Where: t = landfill gas production at a given time [m3LFG.y-1] = dissimilation factor 0.58 [-] 1.87 = conversion factor [m3LFG.kgCdegraded-1] A = amount of waste in place [Mg] Co = amount of organic carbon in waste [kg C.Mg waste-1] k1 = degradation rate constant 0.094 [y-1] t = time elapsed since depositing [y]
21.2 – Prognosis of landfill gas production
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21 – Landfill gas
First order model – organic content
Waste category Organic carbon content [kgC.Mg-1] Contaminated soil 11 Construction & demolition waste 11 Shredder waste 130 Street cleansing waste 90 Sewage sludge & compost 90 Coarse household waste 130 Commercial waste 111 Household waste 130
21.2 – Prognosis of landfill gas production
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21 – Landfill gas
Multi phase first order
3
1,1,0
,1
i
tkiit
iekcAC
Where: t = landfill gas production at a given time [m3LFG.yr-1] = dissimilation factor [-]* i = waste fraction with degradation rate k1,i [kgi.kgwaste
-1]** c = conversion factor [m3LFG.kgOMdegraded
-1]*** A = amount of waste in place [Mg] Co = amount of organic matter in waste [kgOM.Mg waste-1] k1,i = degradation rate constant of fraction i [y-1]* t = time elapsed since depositing [y]
21.2 – Prognosis of landfill gas production
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Multi phase first order – organic content
Waste category Minimum organic matter content [kgOM.Mg-1]
Maximum organic matter content [kgOM.Mg-1]
Rap Mod Slow Total Rap Mod Slow Total
CS: contaminated soil 0 2 6 40 0 3 8 42
C&D: construction & demolition 0 6 12 44 0 8 16 46
SW: shredder waste 0 6 18 60 0 11 25 70
SCW: street cleansing waste 9 18 27 90 12 22 40 100
S&C: sewage sludge & compost 8 38 45 150 11 45 48 160
cHW: coarse household waste 13 39 104 260 19 49 108 270
CW: commercial waste 13 52 104 260 19 54 108 270
HW: household waste 60 75 45 300 70 90 48 320
21.2 – Prognosis of landfill gas production
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21 – Landfill gas
Organic matter and Organic C
)/132()/48()/72/180(
33 246126
molgmolgmolgCmolgOM
COCHOHC
Therefore:
Methane and LFG production per kgOM degraded: LFGmCHm 3
43 75.0373.0
714180
48
Methane and LFG production per kgC degraded: LFGmCHm 3
43 87.1933.0
71472
48
21.2 – Prognosis of landfill gas production
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21 – Landfill gas
Prognosis of LFG production
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50
100
150
200
250
300
19
65
19
70
19
75
19
80
19
85
19
90
19
95
20
00
20
05
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10
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15
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20
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25
20
30
20
35
(m
³LF
G/h
)
k=0,094 k=0,04
21.2 – Prognosis of landfill gas production
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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
5. Climatic conditions
21.2 – Prognosis of landfill gas production
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21.3 Extraction systems
Lay out of an extraction system
Various types of extraction systems
Recovery efficiency
21.3 – Extraction systems
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21 – Landfill gas
Lay out
flaring and/orutilisation
production
emission
oxidation
extraction
21.3 – Extraction systems
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21 – Landfill gas
Various types of extraction systems
1.Vertical
2.Horizontal
3.Slope
4.Point
21.3 – Extraction systems
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21 – Landfill gas
Vertical
Conventional Cell wise
Build up Build up + early extractionGRAVEL
HDPE piping (perforated)
HDPE piping (non -perforated)
21.3 – Extraction systems
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21 – Landfill gas
Gas well connection
RULE OF THUMB: 4 GAS WELLS PER HA
21.3 – Extraction systems
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21 – Landfill gas
Recovery efficiency
Disposal phase Recover efficiency
Straight after disposal PHASE 0 - (=0%)
During start up period exploitation phase PHASE 1 10% - 25% Exploitation phase PHASE 2 25% - 50% After the First year of the exploitation phase untill final top cover
PHASE 3 50% - 60%
Temporary cover and covering of slopes PHASE 4 60% - 75% After ending exploitation phase, landfill fully covered
PHASE 5 70% - 80%
Final situation after completion, liner system in tact and in operation
PHASE 6 90% - 100%
21.3 – Extraction systems
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21.4 Production monitoring
Monitoring equipment
Anemo meter Digital mano meter
Gas analyser
21.4 – Production monitoring
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Gas analyser can measure:
1. CH4
2. CO2
3. O2
4. N2 (= 100% - CH4% - CO2% - O2%)
21.4 – Production monitoring
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If CH4 and O2 concentration respectively in a gas
well is:
> 50% and < 1% then more extraction
< 50% and > 1% then less extraction
21.4 – Production monitoring
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If N2:O2 ratio is:
> 5 indicator suction of ambient air
< 4 indicator leakage piping extraction system
21.4 – Production monitoring
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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
21.5 – Flaring, electricity and heat production
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21 – Landfill gas
Flaring
Open flare
Enclosed flares
Passive flare
21.5 – Flaring, electricity and heat production
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21 – Landfill gas
Heat production
LFG fired boilers
Heat exchangers WWTP
21.5 – Flaring, electricity and heat production