Transcript Document

TSEC Biosys
TSEC Biosys
TSEC-BIOSYS:
A whole systems approach to bioenergy
demand and supply
www.tsec-biosys.ac.uk
Richard Murphy
Imperial College London
Biomass role in the UK energy futures
The Royal Society, London: 28th & 29th July 2009
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TSEC Biosys
TSEC Biosys
Sustainability issues: a focus on
Biodiversity, water use and life-cycle GHG
balances
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Biomass and sustainability
The overall ‘sustainability’ of biomass use in the UK is
affected by numerous issues e.g.
– Direct and indirect land use
– Greenhouse gas balances
– Water use in agriculture and forestry
– Biodiversity protection and management
– Transport impacts
– Rural economy and livelihoods
– Waste management
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TSEC Biosys
Aim
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TSEC Biosys
TSEC BIOSYS has focussed on analysing and quantifying
3 key attributes of the environmental sustainability of
biomass energy systems for the UK
– Influence of perennial biomass crop production on
biodiversity indicators (SRC willow,)
– Water consumption of perennial biomass crops
(Miscanthus)
– Life-cycle greenhouse gas balances for a range of
UK and imported biomass sources – both pre-harvest
and whole life-cycle analyses
Biodiversity
Work conducted in Theme 2 by Rebecca Rowe, Univ. Southampton
Limitation of previous Willow SRC biodiversity studies:
•
Small or non-commercial sites – little on commercial
•
Few direct comparison between SRC and arable land and
none for set-aside land.
•
Limited number of species
(birds, pest species)
•
Few studies on ecosystem
processes
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Biodiversity
• Three field investigations on willow SRC, Arable and
set-aside land:• 2006: Comparison of flying invertebrate and ground flora
diversity and abundance between
• 2007: Comparison of ecosystem process of herbivory,
decomposition and predation
• 2008: Detailed investigation of predation pressure
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Key findings: Plants (example)
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Species Richness & Abundance
• Species richness
– Similar in all headlands
– In the cultivated area set-aside land > willow SRC > arable land
• Ground flora biomass
– Similar in set-aside and willow SRC, reduced in arable land
Key findings: Predation (example)
• Predation rates highest in arable land > willow SRC >
set-aside for both small mammals and ground
invertebrates
Predation pressure
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Main Conclusions - Biodiversity
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• In agricultural landscapes, willow SRC increased farmscale biodiversity.
• Willow SRC provides a more stable, less intensive
environment for plants, invertebrate and small
mammals which are uncommon in arable land.
• Willow SRC provides a breeding site for several small
mammal species
• The effect of willow SRC on ecosystem process are
significant and complex.
Water
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TSEC Biosys
Work conducted in Theme 2 by John Finch, CEH
Main focus: What are the potential impacts of energy crops on
water resources?
• Water quality is not a significant unknown:
– Biomass crops have lower inputs so are positive;
– Concerns about sediment mobilisation are unlikely to be
realised;
– Biofuel crops = status quo;
• A major concern is water resources:
– High yield = high water use.
Water
New data collected from field measurements for Miscanthus and
model developed
Miscanthus compared
with other bioenergy
crops, arable crops,
grassland and woodland
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TSEC Biosys
Water
•
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The annual harvests leave a period of a couple of months, in the
spring, when the substrate is exposed – so evaporation occurs;
• Leaf fall into January so
there is storage for
interception losses;
• The deep roots provide
soil water to support
transpiration in summer;
• Miscanthus seems less
sensitive to soil water stress
than the other vegetation
types.
Main Conclusions - Water
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TSEC Biosys
For the soil and climatology of the site:
• The annual water use of Miscanthus is comparable to that of
permanent woodland;
• The annual water use of SRC willow is comparable to that of
winter wheat;
• Both are higher than permanent grassland
But
• More field validation needs to be done;
• The model can then be run in a spatially distributed form for
various crop distributions.
Life Cycle GHG balances
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TSEC Biosys
Work led in Theme 2 by Jon Hillier and Pete Smith and in Theme 3 by
Carly Whittaker, Nigel Mortimer and Richard Murphy.
Main focus: To what extent can energy from biomass contribute
to meeting the UK’s greenhouse gas targets?
A TSEC-BIOSYS Life Cycle Assessment (LCA) model was developed:- Utilises current, UK-specific case studies
- Encompasses relevant UK biomass supply chains
(including some imported biomass)
- Scope for future scenarios and varying scales of energy
production
Pre-harvest GHG balances
- role of soil in the GHG balance
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TSEC Biosys
• The soil C pool is the
balance of accumulated inputs
and emissions
• C inputs depend mainly on
plants growing on the soil
• C emissions depend mainly
on the size of the C pool
• Under constant land use
tends to an equilibrium where
C inputs balance emissions
Average equilibrium soil C:



SRC ~110 t/ha
Miscanthus ~100 t/ha
Winter wheat ~45 t/ha
OSR, ~55 t/ha
Pre-harvest GHGs
•
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Previous literature based analysis (St Clair et al 2008) of
pre-harvest GHG balance (management and soil
balance) generated 4 ‘rules’ :1.
2.
3.
4.
Don’t replace woodland with any bioenergy crop
Don’t replace grasslands with OSR or winter wheat
SRC and Miscanthus on arable are OK
OSR and WW on arable land is neutral
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Yield map
C inputs
Climate maps
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Soil
variable
maps
RothC
GHG balance Map
Pre-harvest GHGs
GHG balance including
emissions from
farming
(machinery,
fertiliser, crop
protection)
Predicted soil emissions/sequestration
For 4 bioenergy crops. Annualised 20
Year average using RothC
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Pre-harvest GHGs: Summary
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• Revised analysis in TSEC-BIOSYS enhances these
‘4 rules’ for UK
1. Don’t replace woodland with any bioenergy crop - emission of
up to 4 CO2eqt/ha/year
2. Don’t replace grasslands with OSR or winter wheat - net
emissions ~ 1 CO2eqt/ha/year
3. SRC and Miscanthus on arable and grassland saves up to ~4-5
CO2eqt/ha/year
4. OSR and winter wheat on arable land is neutral


Key sensitivites Crop yield, Fertiliser usage, and Soil C
balance (previous land use) – geographic location
There is a strong need for soil C data under Miscanthus
and SRC for a range of soil types and climates
TSEC LCA GHG balances
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TS E C
TSEC Biosys
(whole life-cycle) AIMS
• Review and integrate relevant studies on carbon balances of
bioenergy supply chains
Life Cycle Analysis approach
• Produce coherent model applicable to the UK bioenergy
sector
Sector not yet fully developed…Examine biomass projects in
operation now
Produce flexible model
• Assess carbon abatement ‘wedges’ for the UK
Depends on supply and end-use.
Produce series of multipliers (e.g Kg CO2/MWh or /ODT)
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TSEC LCA Model (whole life-cycle)
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TS E C
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• Covers :
– 15 biomass supply chains
– Land-use reference system (set-aside, grassland, managed
grassland)
– 5 Waste/residue reference systems (incl. mulching, heat
production, landfill, fertilizer addition)
– 10 Transport options (7 Truck, 2 Train, Marine)
– 4 Outputs (Electricity, Heat, CHP, or Co-fired electricity)
Output: Energy requirement and GHG emissions for specific supply
chain with detailed breakdown of where all emissions occur
Case Studies: Supply Chains
Consumers:
• Co-firing – Drax
• Dedicated electricity – Wilton 10
• District heating – Barnsley
• CHP – Literature
Suppliers:
• Miscanthus – Bical
• SRC– Renewable Energy Growers
• Forest Residues – Forestry Commission
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Forest residue extraction
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(example)
The yield of forest resides
on a particular site depends on
tree species and yield class.
Yields estimated using Forestry
Commission’s BSORT model
through a series of mass flow
partitions to give biomass yield at
each harvesting event throughout
the rotation of the forest
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TS E C
TSEC Biosys
11 Tree Species
4-6 Yield Class Ranges
28 UK Regions
Volume-dependent transport emissions
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TS E C
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- a new UK dataset from TSEC-BIOSYS
Based on biomass bulk densities + vehicle volume capacities
0.3
0.25
0.2
0.15
0.1
0.05
Road
Pellets
Electric
Diesel
5.5
7.5
18
26
32
40
0
44
KG CO2 eq./t-km
0.35
Rail
Chips
Bales
Marine
Land-use change and Carbon sequestration
- integration TSEC-BIOSYS Theme 2 and Theme 3
TS E C
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6
4
2
0
-2
-4
GHG benefit
Replace arable
soil
Replace Grassland
incl. prev. LU management
with oilseed
rape
with winter
wheat
with SRC poplar
with Miscanthus
with oilseed
rape
with winter
wheat
with SRC poplar
with Miscanthus
with oilseed
rape
with winter
wheat
with SRC poplar
-6
with Miscanthus
Annual net emissions, t CE ha
-1
GHG cost
Replace Forest/Semi-natural
incl. fossil fuel displaced
Waste Wood and
Arboricultural Arisings
Waste
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-No value to anyone anywhere
-Would have been disposed Landfill
Kg CO2 eq/tonne Landfilled (100
Year Time Frame)
2500
-Collection
SOURCE
2000
-Reference system?
1500
DEFRA
WRATE
1000
500
Damen & Faaij,2003
0
-500 0%
20%
-2000
IPCC
60%default
80%
Mann & Spath,2001
-1000
-1500
40%
Gardner et al., 2002
SINK
Degradation Rate of Landfilled Wood (% )
Carbon Sequestered
Electriciy Credits
Methane Emissions
Overall Greenhouse Gas Balance
100%
Net sink or
source?
Highly sensitive
to degradation
rate
Main Conclusions: GHG balances
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TS E C
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• Variability
– Overall ‘greenhouse gas footprint’ is determined by a
several factors and LCA ‘decisions’
Uncertainty can be found in
• LCA methodology and decisions
– Allocation procedures between co-products
– Land-use reference system
– Substitution/Avoided emissions
• Data and constraints
– Effects of residue removal on sustainability
– Landfill behaviour (waste wood)
– N2O emissions from soil
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…Kg CO2 eq. ‘per ODT biomass’
• Can depend on many factors
– Quantifiable things
•
•
•
•
Inputs
Yield
Moisture Content
Material losses
– Methodology Decisions:
• Landfill behaviour
• Land use change
• Reference system
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LCA Model
is flexible
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Emission Savings
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E.g. SRC chips
% Savings CO2 eq.
savings?
Compared to?
Biomass
Required Per
Year
Co-firing (10%)
9%
3,191,301
Coal
3,726,898
Dedicated
Electricity
92%
165,048
Grid electricity
300,000
CHP (Electricity)
94%
33,181
Grid electricity
54,000
CHP (Heat)
97%
59,519
Natural Gas
54,000
Heat alone
94%
331
Natural Gas
500
Overall Emissions
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Biomass- electricity can offer significant savings
--Best generated as part of a CHP system
- Shares plant construction etc. with heat output
-Co-fired electricity is low but still burns coal
E.g. SRC chips
1000
900
Emissions (Kg Co2 eq./MWhe or t)
800
700
600
500
400
Heat is ‘best’ use for biomass
- High conversion efficiency
-Lower overall emissions per MWh
300
Per MWh
200
100
0
Heat (alone) Heat (CHP)
Heat
Heat
(Natural
Gas)
Electricity
(CHP)
Electricity
(Dedicated)
Electricity
(Co-firing
biomass)
Electricity
(Co-firing
coal +
biomass)
Electricity
Electricity
(Natural
Gas)
Electricity
(Grid)
Electricity
(Coal Fired)
Summary: GHG balances
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TS E C
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• Significant savings in GHG emissions available from a
wide variety of biomass energy options
• Savings dependent on specifics of the pre-harvest
systems and the supply chain, including what is
displaced
• Highly flexible models and tools available for
optimisation and forward looking analyses
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TS E C
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Report available
August 09
Overall Summary
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TS E C
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Bios ys
• Perennial bioenergy crops (SRC willow example)
can support biodiversity in the agricultural
landscape
• Water demands for bioenergy crops (Miscanthus
example) are broadly similar to other agriculture &
forest land uses
• Significant savings in GHG emissions available from
a wide variety of biomass energy options
Acknowledgements
TSERC-BIOSYS Researchers:Carly Whittaker, Jon Hillier, Rebecca Rowe,
Philip Sinclair, Sophie Jablonski
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TS E C
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Bios ys
Thank you
TSEC Biosys
TSEC Biosys
TSEC Biosys
TSEC Biosys
www.tsec-biosys.ac.uk
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