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Projections of GHG emissions and effects of policies and measures in the waste sector in
the United Kingdom
Presented by
Robert G Gregory
Introduction
The UK’s National Assessment Model for assessing methane emissions from landfills was constructed in 1999
It was updated and revised in 2002
New estimates of national emissions and forecasts were made under a number of waste management scenarios
The approach taken is consistent with IPCC Guidelines and IPCC Good Practice guidance (IPCC, 1996; 2000)
It takes account of the flexibility allowed in the IPCC guidance for site/country specific data/information and sound scientific principles to be accommodated
Background to the UK model
The model implements the IPCC (1996) Tier 2 equations
Additional enhancements come from the following:
Three methane generation rate constants, k, are adopted for different degradabilities of waste
Commercial and Industrial (C&I) waste streams have been introduced alongside municipal solid waste (MSW)
Different methane generating potential terms are used for MSW and C&I wastes
Background to the UK model
Four different landfill site types are simulated
each has different degrees of engineering and gas collection
these represent the evolution of landfill engineering and landfill gas management in the UK since 1945
Alignment with GasSim
The Environment Agency for England and Wales uses GasSim for the regulation of all its operational landfills
GasSim is a state of the art model GasSim has been described by Iain
Whitwell on Day 1 of this Workshop The 2002 revisions to the National
Assessment Model aligns this model with the scientific principles implemented in GasSim
Waste Related Revisions
Waste degradation rate constants are now aligned with GasSim
The methane generating potential, L0(x), is a function of Organic Carbon (DOC) and Fraction Dissimilated (DOCF)
DOC and DOCF are specific to the individual components of the waste (e.g. paper, textiles, food waste, etc)
DOC and DOCF are now calculated for the individual waste components in the waste stream and then summed
values were based on well-documented US research for the USEPA’s life-cycle programme, adapted to UK conditions
Methane Oxidation Model
A methane oxidation model was built on a number of simple underlying concepts:
the surface soil cover must be sufficiently thick and/or the methane flux must be sufficiently low to permit a significant amount of methane oxidation to take place within the cap
methane oxidation takes place in the soil cap if the soil depth > 0.3m for modern lined landfills, or
If the soil depth > 1.0m for old unlined landfills
If neither condition is met, no methane oxidation will take place
The methane available for oxidation in the cap is determined after the quantity that is utilised or flared (i.e. recovered) is subtracted from the methane generated
Methane Oxidation Model
No oxidation in fissure flow
Cap with a maximum oxidising capacity
Small source term
Large source term
Small or large source term
Methane Oxidation Model
The methane available for oxidation is defined as:
where
Avail oxd cap = methane available for oxidation in year x
fissure = fraction of methane lost through fissures
CH4 generated(x) = methane generated in year x (kt/y)
R(t) = methane recovered in year x (kt/y)
The model output is most sensitive to the values for field oxidation efficiency and the fraction lost through fissures
)t(R)x(generatedCH1)x(Avail 4fissurecapoxd
Methane Oxidation Model
The fraction of methane that is oxidised can be limited by either
the sink capacity of the soil (the methane oxidising capacity of the soil cover)
or the quantity of methane available for potential oxidation
)x(generatedCH
)t(R)x(generatedCH1OX
4
4fissure
)x(generatedCH
Soil1OX
4
capoxdfissure
Landfill Gas Management
Installed flare capacity suggests that only 1/3 of all capacity is associated with power generation facilities
Growth in installed flare capacity 1980 - 2000
0
100
200
300
400
500
600
700
800
1980 1985 1990 1995 2000 2005
1000
's m
3 L
FG
/h
Installed
Operational
Standby
Landfill Gas Management
Installed generation capacity is greater than back-up flaring capacity
Power generation facilities do not have equal capacity of back-up flaring
Growth in installed generation capacity 1980 - 2005
0
50
100
150
200
250
300
350
400
1980 1985 1990 1995 2000 2005
Land
fill g
as c
apac
ity (1
000'
s m
3 LFG
/h)
Installed generationcapacity
Installed backupflaring capacity
Scenario Development
Eight MSW scenarios were developed to investigate various waste management options
Achieving LD targets with current material recycling rates
Achieving LD targets with emphasis on paper/compost recycling
Achieving LD targets with emphasis on paper recycling
Achieving LD targets with emphasis on EfW/CHP/AD
Achieving Waste Strategy 2000 targets with emphasis on glass metals and plastics recycling
Higher growth rate, achieving LD targets with current material recycling rates and excess EfW/CHP/AD
Higher growth rate, achieving LD targets with excess material recycling rates
Current (2000) trends in diversion continued (Base case) – unlikely to achieve LD target
Scenario Development
Five additional C&I scenarios were developed Baseline - current landfill 15% diversion based on food wastes,
paper & card and other biodegradables to AD, EfW and recycling (lose readily degradables from total C&I excluding C&D)
15% diversion based on general biodegradable wastes to combustion (lose readily and moderately degradable organics)
15% diversion based on general biodegradable wastes to recycling (lose readily and moderately degradable organics)
15% diversion through C&D and mineral wastes recycling (lose inerts)
LFG Generated, Emitted, and Measured
Historic Landfill Gas Generation/ Emission Forecasts
ETSU 1996
AEAT 1999 NPL 1997
emissions calibration data
LQM 2002 0
500
1000
1500
2000
2500
3000
3500
4000
1945
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
2020
2025
Met
hane
(kt)
ETSUfit generated
ETSUfit emitted
AEAT (1999) generated
AEAT (1999) emitted
LQM (2002) generated
LQM (2002) emitted
NPL study
Calibrating the Methane Oxidation Model
Sensitivity of the fissure term in the Methane Oxidation Model
The IPCC 10% oxidation default exceeds observed data
Fissures could account for 1% to 30% of the losses and be within the window of measured data
0
500
1000
1500
2000
2500
3000
3500
4000
1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025
Met
hane
(kt )
LQM Base casegenerated
LQM 10% IPCCBase case emitted
0.01
0.1
0.3
0.5
0.75
NPL study
Calibrating the Methane Oxidation Model
Effect of the field efficiency term in the Methane Oxidation Model
Field efficiency could be between 40% and 100% and be within the window of measured data
0
500
1000
1500
2000
2500
3000
3500
4000
1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025
Met
hane
(kt)
LQM Base casegenerated
LQM 10% IPCCBase case emitted
0.1
0.2
0.3
0.5
0.75
1
NPL study
Results of Scenario Modelling
The effect on Methane Generation/ Emissions resulting from the various future MSW Scenarios 1 – 8 (with C&I Scenario 1 fixed) period 1945 – 2025
0
500
1000
1500
2000
2500
3000
3500
4000
1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025
Met
hane
(kt)
Total gen S8_1
Total gen S7_1
Total gen S6_1
Total gen S5_1
Total gen S4_1
Total gen S3_1
Total gen S2_1
Total gen S1_1
ERM em S8_1
ERM em S7_1
ERM em S6_1
ERM em S5_1
ERM em S4_1
ERM em S3_1
ERM em S2_1
ERM em S1_1
Results of Scenario Modelling
The effect on Methane Generation/ Emissions of resulting from the various C&I Scenarios 1 – 5 (with MSW Scenario 8 fixed) period 1945 – 2025
0
500
1000
1500
2000
2500
3000
3500
4000
1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025
Met
hane
(kt
)Total gen S8_1
Total gen S8_2
Total gen S8_3
Total gen S8_4
Total gen S8_5
ERM em S8_1
ERM em S8_2
ERM em S8_3
ERM em S8_4
ERM em S8_5
LFG recovery is the greatest sink
LFG utilisation is encouraged by the Landfill Directive and Renewable Energy subsidies
This far outweighs the impact of future diversion policies in the UK because of the size of the existing LFG resource
0
500
1000
1500
2000
2500
3000
3500
4000
1945
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
2020
2025
Met
hane
(kt)
LQM (2002)generated
CH4 recovered
Summary
All the MSW strategies considered achieved some benefit in methane emissions reduction compared with the base cases (Business as Usual)
The most significant scenario is paper recycling
a 19% reduction in residual methane emissions by 2025 (31 kt CH4 abated)
Summary
The effects of the diversion strategies were not as significant as the impact on emissions reduction due to flaring or gas utilisation
methane abated by flaring or utilisation is 1750 kt in 2000, rising to 2465 kt in 2005
The impact of any of the C&I scenarios compared to the base case were negligible in terms of methane emissions abatement.
