Post on 21-Jan-2016
description
Climate Effects of Woody Biomass Systems
Leif GustavssonLinnaeus University
Sweden
Bioenergy Australia 2013
Building the future - Biomass for the Environment, Economy and Society 25 - 26 November, 2013
Crowne Plaza Hunter Valle, Australia
Global primary energy use in 2010 (≈500 Exajoule)
• Oil 32.4%
• Coal 27.3%
• Gas 21.4%
• Total fossil 81.1%
• Bioenergy 10.0%
• Nuclear 5.7%
• Total fuel 96.8%
• Other 3.2%
Exa = 1018
Source: International Energy Agency, 2012. Key World Energy Statistics
Primary energy use in IEA “New Policies” scenario
Source: International Energy Agency, 2011. World Energy Outlook 2011.
EJ/
yr
Legend
Sweden
Europe
0 750 1,500375
Kilometers
69° N69° N
66° N66° N
63° N63° N
60° N60° N
57° N57° N
Legend
Jämtland and Västernorrland
0 250 500125
Kilometers
Example: Forest residues substitute fossil fuels
Forest residues (slash) substitute different fossil fuels in stationary plants at different locations
• A system analysis from forest area to local (80km), national (600km) and international (1100km) large end-users
• Functional unit is 1 MWh of delivered wood chips at the local, national and international large end-users
• Data on forest residues based on experience in central Sweden
• Fuel cycle fossil emissions are considered
Reduced fossil CO2 emission if slash substitutes fossil fuels in stationary plants at different locations
-2
0
2
4
6
8
10
12
Naturalgas
Oil Coal
CO
2-b
alan
ce (
ton
ne
C/h
a)
Local
National
International
Primary energy
Source: Gustavsson L, Eriksson L, Sathre R. 2011. Costs and CO2 benefits of recovering, refining and transporting logging residues for fossil fuel replacement. Applied Energy 88(1): 192-197.
Example: Forest residues substitute fossil fuels
Fossil system1. Fossil fuels are used for energy
2. Forest residues are left in forest and gradually decay
Bioenergy system1. Fossil fuels are used for biomass harvest and logistics
2. Forest residues are used for energy
We consider annual GHG emissions including biogenic carbon emissions
Physical,ecological,and social
disturbances
Anthropogenic climate change:Chain of events
Mean temperature
change
Radiative forcing
•GHG emissions
•Albedo change
•Aerosols•Ozone
Human activities
(IPCC 2007)
Emissions time profile influence the climate impact
Greenhouse gasesLongwave radiation
(e.g. heat)
Shortwave radiation(e.g. light)
• Integrated over time, cumulative radiative forcing (CRF) is W-s/m2, i.e. trapped energy per area – a proxy for temperature increase
•The longer a GHG is in the atmosphere the more energy is trapped and the more climate change occurs
Greenhouse gases cause an imbalance between incoming and outgoing radiation - “radiative forcing” heat is trapped
Figure not to scale!
Atmospheric decay of unit pulses of GHGs
186.151.189.1722 186.0338.0259.0217.0)(
ttt
t eeeCO
1142 )(
t
t eON
124 )(
t
t eCH
N2O
CO2
CH4
Years
(IPCC 1997, 2001, 2007)
Radiative forcing (W/m2) due to GHG concentration change
ref
CO CO
COF
2
21ln)2ln(
7.32
where CO2ref = 383ppmv, N2Oref = 319ppbv, CH4ref = 1774ppbv
• Assumes relatively minor marginal changes in GHG concentrations
• Spectral overlap between N2O and CH4 is accounted for
• Radiative forcing not related to GHGs (e.g. albedo change) is not considered
(IPCC 1997, 2001, 2007)
),(12.0 2222NMfONONONF refrefON
),(036.0 4444NMfCHCHCHF refrefCH
Changed cumulative radiative forcing per ton of dry biomass when slash substitute fossil fuels
Adapted from: Sathre R. and Gustavsson L. 2011. Time-dependent climate benefits of using forest residues to substitute fossil fuels. Biomass and Bioenergy 35(7): 2506-2516.
Changed cumulative radiative forcing per ton of dry biomass when slash substitute fossil fuels
Adapted from: Sathre R. and Gustavsson L. 2011. Time-dependent climate benefits of using forest residues to substitute fossil fuels. Biomass and Bioenergy 35(7): 2506-2516.
Changed cumulative radiative forcing when slash substitute fossil coal – sensitivity analysis of energy input for harvest and
transport
Adapted from: Sathre R. and Gustavsson L. 2011. Time-dependent climate benefits of using forest residues to substitute fossil fuels. Biomass and Bioenergy 35(7): 2506-2516.
Comparison of biomass and fossil systems
The same energy and housing service from both of the systemsCRF is calculated based on difference in annual GHG emissions between systems
Forest strategy: harvest biomass
Woody Biomass System Reference Fossil System
Forest land
Forest strategy:carbon storage
Forest land
3) Unmanaged and non-harvested management with 20 % increase (3a) and with 20 % decrease (3b)
Fossil coal is used for heat and power
production, concrete frame in
building construction
Woody biomass is used for heat and power production,
wood frame in building
construction
1) Conventional management with 109-year rotation2) Fertilized management with 69-year rotation
Forest biomass replace concrete constructions – An apartment building example
4 stories, 16 apartments, 1190 usable m2
Built in Växjö, Sweden
Case-study building:Wood frame
Reference building:Reinforced-concrete frame
Hypothetical building with identical size and function
• Fossil CO2 emission from primary energy use for production
and distribution of building materials and for assembly and demolition of buildings
• CO2 balance of cement reactions (calcination and carbonation)
• Use of biomass by-products from forestry and wood processing
• Carbon storage in wood products
• Carbon stocks and flows in forest
• End-of-life management
CO2 balance of building production and of end-life
Forest management and growth
•Starting point:•A mature Norway spruce stand located in northern Sweden conventionally managed with a 109-year rotation period
•Three forest management alternatives:
1.Clear-cut harvest followed by continuation of conventional management with 109-year rotation period
2.Clear-cut harvest followed by fertilised management with 69-year rotation period
3.Stand is left unharvested and unmanaged with carbon stock stabilizing at
(a) 20% below or (b) 20% above conventional harvest level
(rough assumption)
Decay of biomass left in forest
•We assume decay into CO2 at a negative exponential rate
•Decay constants of:
-0.033 for small-diameter logs (Næsset 1999)
-0.046 for stumps and coarse roots (Melin et al. 2009)
-0.074 for branches and tops (Palviainen et al. 2004)
-0.129 for fine roots (Palviainen et al. 2004)
-0.170 for needles (Palviainen et al. 2004)
Several uncertainties
0
50
100
150
200
250
300
350
0 20 40 60 80 100 120 140 160 180 200 220 240
Livi
ng tr
ee b
iom
ass
(tC/
ha)
Time (Years)
ConventionalFertilizedUnmanaged (low)Unmanaged (high)
Stand level living tree biomass stock for the different forest management regimes
Source: Haus, S., Gustavsson, L., Sathre, R. (2013). Climate Mitigation Comparison of Woody Biomass Systems with the Inclusion of Land-use in the Reference Fossil System (Journal manuscript)..
Stand level CRF for conventional and fertilized forest management
Based on the difference in GHG between the fossil and the biomass system with varied forest carbon stock in fossil system
Source: Haus, S., Gustavsson, L., Sathre, R. (2013). Climate Mitigation Comparison of Woody Biomass Systems with the Inclusion of Land-use in the Reference Fossil System (Journal manuscript)..
-22
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
0 20 40 60 80 100 120 140 160 180 200 220 240
CRF
(W s
/m2
per h
a)
Conventional management
Fertilized management
Stand level CRF for conventional and fertilized forest management – The black line with excluded forest land-use in reference system
Based on the difference in GHG between the fossil and the biomass system
Source: Haus, S., Gustavsson, L., Sathre, R. (2013). Climate Mitigation Comparison of Woody Biomass Systems with the Inclusion of Land-use in the Reference Fossil System (Journal manuscript)..
-22
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
0 20 40 60 80 100 120 140 160 180 200 220 240
CRF
(W s
/m2
per h
a)
Conventional management
Fertilized management
Primary energy use in Sweden 2010
166
68
135
26
190Oil and oil products
Narural gas (18)Coal and coke
Biofuel, peat, etc.
Hydro power
Nuclear power
Wind power (4)
Pumped heat (5)
Heat plants
Electricity production*
Other sectors
Pulp and paper industry
Residential, service, etc.
35%
12%
37%
13%
TWh
*in both industry and district heating sectors
Source: Energy in Sweden 2012, Swedish Energy Agency
Annual Swedish bioenergy use
Source: Swedish Energy Agency: Energy in Sweden 2009, and Kortsiktsprognos 2010
Standing stem volume on Swedish productive forest land and scenarios for 2010 - 2110
0
1000
2000
3000
4000
5000
1950 1970 1990 2010 2030 2050 2070 2090 2110Year
Mill
ion
m3
ste
m v
olu
me
ove
r b
ark
Environmental scenario
Production scenario
Reference scenario
Historic data
Source: Skogsstyrelsen, Skogliga konsekvensanalyser och virkesbalanser 2008
• Climate benefits of forest residue use depends strongly on the fossil energy system that is substituted
• Substituting coal in stationary plants consistently results in large climate benefits
• Substituting transportation fuels results in initial climate impacts, followed by modest long-term climate benefits
• Long-distance transport of forest residues has a minor impact on climate benefits
Conclusions/discussion
Conclusions/discussion
• The radiative forcing from forest management emissions is very low
• The material and energy substitution effects dominate the climate benefits
• Forest fertilization can significantly increase biomass production
• Climate benefits from material and energy substitution significantly increase when forest fertilization is use