1

TSEC-BIOSYS: A whole systems approach to bioenergy

demand and supplywww.tsec-biosys.ac.uk

Carly WhittakerImperial College/North Energy Associates

carly.whittaker@northenergy.co.uk

Biomass role in the UK energy futures The Royal Society, London: 28th & 29th July 2009

TSEC BiosysTSEC Biosys

TSEC BiosysTSEC Biosys

Topic 3.2. Full supply chain greenhouse gas (GHG) emissions assessment

TSEC Biosys

Carly Whittaker Dr Richard MurphyDr Nigel Mortimer

Topic 2.3 – Pre-harvest GHG balance of energy crops

Dr Jon HillerProf. Pete Smith

Aims of work• Review and integrate relevant studies on carbon balances of

bioenergy supply chainsLife Cycle Analysis approach

• Produce coherent model applicable to the UK bioenergy sectorSector not yet fully developed…Examine biomass projects in

operation nowProduce flexible model

• Assess carbon abatement ‘wedges’ for the UKDepends on supply and end-use. Produce series of multipliers (e.g Kg CO2/MWh or /ODT)

TSEC Biosys

Case Studies: Supply ChainsConsumers:• Co-firing – Drax • Dedicated electricity – Wilton 10 • District heating – Barnsley• CHP – plan b: Literature Suppliers:• Miscanthus – Bical • SRC– Renewable Energy Growers • Forest Residues – Forestry Commission

TSEC Biosys

LCA: Systems Boundaries of ModelTSEC Biosys

Biomass feedstock production

Conversion to energy

Processing

Transport Storage

On-site Processing

• Overall GHG savings depends on overall GHG of biomass supply chain• Define relevant supply chain stages • Significant data collection required to quantify:

– Direct & Indirect energy consumption/emissions:• Fossil fuels • Manufacture of consumed materials• Construction of machines/buildings/vehicles

Kg CO2 eq.

Kg CO2 eq.

Kg CO2 eq.

Kg CO2eq

MJ Natural Gas

MJ Diesel

MJ Diesel

MJ Grid Electricity

Stuff Construction

ConstructionVehiclesFertilizers

Machines

Kg CO2 eq.

Material Losses

Material Losses

Material Losses

Machines

tonnes MWh e/t

TSEC-LCA-ModelFully transparent model- (MS Excel)- Can be replicated or updated with improvements in

knowledge• Covers :

– 15 Types biomass– 3 Land-use reference systems– 3 Waste reference systems– 10 Transport options– Outputs:

• ‘To the farm gate’ – per tonne @ m.c• ‘To factory/power station gate’- per tonne processed• End use: Electricity, heat, CHP, or co-fired electricity

Output: Energy requirement and GHG emissions profile specific to your

supply chainBreakdown of where all emissions occur

TSEC Biosys

Output: Energy requirement and GHG emissions profile specific to your

supply chainBreakdown of where all emissions occur

-20% 0% 20% 40% 60% 80% 100%

Primary Energy

Carbon Dioxide Emissions

Methane Emissions

Nitrous Oxide Emissions

Total GHG Emissions

Input Material Fuel Delivery to Fuel Hub Storage

Processing Combustion Power Station Construction

Power Station Maintenance Start Up Fuel Ash Disposal

Credit (Fertilizer Displaced) Biomass Reference System

Elements of the Tool TSEC Biosys

1. Biomass Feedstocks:•MJ/Kg CO2 eq. per ODT of:•Miscanthus•Wheat Straw•Forest Residues •Short Rotation Coppice •Waste Wood•Arboricultural Arisings•Olive Residues/Peanut Shells/generic waste•Sunflower Husk Pellets•Dried DDGS•Dried Rape Meal

Stemtips & BranchesSawdustSlabwoodWhole Tree ThinningsRoundwood

11 Tree Species

4-6 Yield Class Ranges

28 Regions UK (road construction intensity

Pellets

Elements of the Tool TSEC Biosys

3 Types of Biomass

•Miscanthus•Wheat Straw•Forest Residues •Short Rotation Coppice •Waste Wood•Arboricultural Arisings•Olive Residues/Peanut Shells/generic waste•Sunflower Husk Pellets•Dried DDGS•Dried Rape Meal

Energy Crops

Co-products

Waste

Each treated in a different way in LCA

With different LCA issues

LAND

Each treated in a different way in LCA

With different LCA issues

TSEC Biosys

Energy Crops

Co-products

Waste

LAND

-Site inputs & operations

-Yield over rotation

-Moisture content

-Land-use reference system

-Carbon sequestration

-Allocation procedure

-No value to anyone anywhere

-Would have been disposed

-Reference system?

0

5

10

15

20

25

1 2 3 4

Scenario

Kg

CO

2 eq

./OD

T

Establishment Fertilizer manufacture Fertilizer application First year cut

Harvesting Termination Emissions from soil

SlurryPK

Slurry NothingArtificialNPK

TSEC Biosys

•Diesel fuel (site establishment and harvesting) most significant sources of emissions - constant

•Artificial fertilizers increase overall emissions

•N=N2O emissions

•Slurry energy requirements transport could be cancelled out

-Site inputs & operations

-Yield over rotation TSEC Biosys

0

50

100

150

200

250

300

350

400

450

7 8 9 10 11 12 13 14 15 16 17 18 19 20

Top Yield (ODT/ha/year)

MJ/

OD

T

0

10

20

30

40

50

60

70

80

Kg

CO

2 eq

./O

DT

-Increase in yield lowers emissions per ODT from shared events

-Harvesting requirements constant

-Not enough known about yield responses to fertilizer

Soil emissions/sequestration depend on Previous land use & proposed new land use

arable arable grassland woodland

OSRSRCMiscanthus

GHG cost

GHG benefit

- Land-use change and Carbon sequestration TSEC Biosys

1) Don’t replace woodlands with any energy crop 2) Also, don’t replace grasslands with OSR 3) SRC & Miscanthus on grassland and arable okay 4) OSR on arable food crop land ~neutral

St. Claire et al., 2008

TSEC Biosys

SRC and Miscanthus generally have better soil C balance than WW or OSR (i.e. they have lower net emissions or higher net sequestration)

Soil GHG emissions are highest in regions where Soil C is currently highest, e.g. Westerly regions, the fens.

So net balance clearly depends both on the bioenergy crop cultivated, and on the initial soil conditions

- Land-use change and Carbon sequestration

TSEC Biosys

(Average) equilibrium soil C of

SRC ~110 t/ha Miscanthus ~100 t/ha WW, ~45 t/ha OSR, ~55 t/ha

- Land-use change and Carbon sequestration

Growing Miscanthus and SRC on arable and grassland leads to GHG saving rather than loss

(up to ~4-5 CO2 equiv t/ha/year)

-6

-4

-2

0

2

4

6

with

Mis

canth

us

with

SR

C p

opla

r

with

win

ter

wheat

with

oils

eed

rape

with

Mis

canth

us

with

SR

C p

opla

r

with

win

ter

wheat

with

oils

eed

rape

with

Mis

canth

us

with

SR

C p

opla

r

with

win

ter

wheat

with

oils

eed

rape

Replace arable Replace Grassland Replace Forest/Semi-natural

An

nu

al n

et

em

issio

ns, t

CE

ha-1

soil incl. prev. LU management incl. fossil fuel displaced

TSEC Biosys

GHG cost

GHG benefit

- Land-use change and Carbon sequestration

Hillier et al., …

Co-Products

TSEC Biosys•Splitting site emissions between products

•Only a real issue when fertilizer inputs are high

0

100

200

300

400

500

600

700

By Mass By Energy Content By Economic Value

Allocation Method

Em

issi

on

s (K

g C

O2

eq./

OD

T)

Straw Wheat

-Allocation

E.g. Wheat Straw

-10

0

10

20

30

40

50

60

Straw pellets (economic) Straw pellets (energy) Straw pellets (mass) % S

avin

gs

Co

mp

ared

to

Nat

ura

l G

as

No Penalty Inc. Penalty

TSEC Biosys

-Allocation

LCA’s that have adopted different allocation procedures cannot be directly compared

E.g. Straw Bales

Economic Energy Mass

Wastes

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

0% 20% 40% 60% 80% 100%

Degradation Rate of Landfilled Wood (%)

Kg

CO

2 e

q/t

on

ne

La

nd

fille

d (

10

0

Ye

ar

Tim

e F

ram

e)

Carbon Sequestered Electriciy Credits

Methane Emissions Overall Greenhouse Gas Balance

SOURCE

SINK

-No value to anyone anywhere

-Would have been disposed

-Collection

-Reference system?

TSEC Biosys

•Waste Wood•Arboricultural Arisings Waste

Mann & Spath,2001

Damen & Faaij,2003

WRATE

Landfill

Net sink or source?

Highly sensitive to degradation rate

DEFRA

IPCC default

Gardner et al., 2002

…Kg CO2 eq. ‘per ODT biomass’

• Can depend on many factors– Quantifiable things

• Inputs• Yield• Moisture Content • Material losses

– Methodology Decisions:• Land use change• Landfill behaviour

TSEC Biosys

TSEC LCA Model is flexible

Transport

0

10

20

30

40

50

60

70

80

90

100

5.5 7.5 18 26 32 40 44

Truck GVW Train Boat

Vehicle

Lo

ad

Fa

cto

r (%

)

Pellets Chips Bales

TSEC Biosys

Volume-based t-km emissions

- Volume database

- Bulk density database

Transport Emissions for - Road - Rail - Marine transport

0.00

0.00

0.00

0.01

0.01

0.01

0.01

5.5 7.5 18 26 32 40 44

Truck GVW

Tran

spor

t em

issi

on (K

g C

O2

eq./G

J-km

)

Pellets Chips Bales

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Pellets Chips

Em

issi

on

s p

er G

J (K

g C

O2

eq./

GJ)

Electricity consumption during processing

GHG Benefit of Pellets vs. chips?

0102030405060708090

0 100 200 300 400 500 600Distance (km)

Em

issi

on

s (K

g C

O2

eq./G

J)

Woodchips Pellets with grid electricity and natural gas

TSEC Biosys

0

10

20

30

40

50

60

70

80

90

0 100 200 300 400 500 600Distance (km)

Ene

rgy

Req

uire

men

t (M

J/G

J)

WoodchipsPellets with grid electricity and natural gas

Electricity and heat generated from forest residues

130 km

1268 km

Biomass heat

-600

-400

-200

0

200

400

600

800

1000E

mis

sio

ns (

Kg

CO

2 e

q./M

Wh

)

Fuel Production Fuel Delivery to Fuel Hub Storage

Processing Combustion Power Station Construction

Per MWh Biomass production phase is where most emissions occurCompared to:- Transport (5-10 Kg CO2/MWh)- Power station construction (15 kg CO2 eq./MWh)- Non-CO2 emissions (15 kg CO2 eq./MWh)

Per M

Wh

TSEC Biosys

Overall Emissions

Overall Emissions TSEC Biosys

0

100

200

300

400

500

600

700

800

900

1000

Heat (alone) Heat (CHP) Heat(Natural

Gas)

Electricity(CHP)

Electricity(Dedicated)

Electricity(Co-firingbiomass)

Electricity(Co-firing

coal +biomass)

Electricity(Natural

Gas)

Electricity(Grid)

Electricity(Coal Fired)

Heat Electricity

Em

issi

on

s (K

g C

o2

eq./M

Wh

e o

r t)

E.g. SRC chips

Per M

Wh

Heat is ‘best’ use for biomass- High conversion efficiency-Lower overall emissions per MWh

Biomass- electricity can offer significant savings-Best generated as part of a CHP system-Co-fired electricity is low but still burns coal

90% 75%

90%

20%30%

40%

40%

50%

40%80 Kg CO2 eq./MWh

160 Kg CO2 eq./MWh

Emission Savings• Overall GHG savings depend on GHG balance of biomass supply

chain - Significant data collection required• LCA’s should be provided in fully transparent manor

– Replicable and updatable• Significant savings can be made with biomass- Key sensitivities are to crop yield, fertiliser usage and land use change- Allocation procedure can vary results- mainly important for high input crops (e.g.

wheat)- Actual emission savings depend on what you are displacing- Heat production provides lowest emissions per MWh and has best conversion

efficiency- Significant greenhouse gas savings can be made with dedicated electricity

generation - Co-firing can also save emissions- but requires large quantities of biomass• Carbon Sink or Sinner? - Depends on previous land use- Overall carbon sequestration with energy crops replacing arable and grassland

TSEC Biosys

TSEC Biosys

Report produced

August 09

29

Thank you for your attention!

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www.tsec-biosys.ac.uk