Transcript Task 38
Climate Effects of Woody Biomass Systems
Leif Gustavsson Linnaeus 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 Coal Gas
Total fossil
Bioenergy Nuclear
Total fuel
Other 32.4% 27.3% 21.4%
81.1%
10.0% 5.7%
96.8%
3.2% Exa = 10 18 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.
Example: Forest residues substitute fossil fuels
69° N
Legend
Jämtland and Västernorrland 69° N 66° N 66° N
Legend
Sweden Europe 63° N 63° N 60° N 60° N 57° N 0 125 250 Kilometers 500 57° N 0 375 750 Kilometers 1,500
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 CO
2
emission if slash substitutes fossil fuels in stationary plants at different locations
12 10 8 6 4 2 0 -2 Natural gas Oil Coal Local National International Primary energy Source: Gustavsson L, Eriksson L, Sathre R. 2011. Costs and CO 2 benefits of recovering, refining and transporting logging residues for fossil fuel replacement.
Applied Energy
88(1): 192-197
.
Example: Forest residues substitute fossil fuels
Bioenergy system
1.
Fossil fuels are used for biomass harvest and logistics 2.
Forest residues are used for energy
Fossil system
1.
Fossil fuels are used for energy 2.
Forest residues are left in forest and gradually decay We consider annual GHG emissions including biogenic carbon emissions
Human activities
Anthropogenic climate change: Chain of events
• GHG emissions • Albedo change • Aerosols • Ozone Radiative forcing
Emissions time profile influence the climate impact
Mean temperature change (IPCC 2007) Physical, ecological, and social disturbances
Greenhouse gases cause an imbalance between incoming and outgoing radiation “radiative forcing” heat is trapped
•Integrated over time,
cumulative radiative forcing (CRF)
is W-s/m 2 , 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
Longwave radiation (e.g. heat) Greenhouse gases Shortwave radiation (e.g. light)
Figure not to scale!
Atmospheric decay of unit pulses of GHGs
(
CO
2 )
t
t
0 .
217 0 .
259
e
172 .
9
t
0 .
338
e
18 .
51
t
0 .
186
e
1 .
186 (
N
2
O
)
t
t
e
114 (
CH
4 )
t
t
e
12 1 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 0 CO CH 25 4 2 N 2 O 50 75 Years 100 125 150 (IPCC 1997, 2001, 2007)
Radiative forcing (W/m
2
) due to GHG concentration change
F CO
2 3 .
7 ln( 2 ) ln 1
CO CO
2
ref
2
F N
2
O
0 .
12
N
2
O
N
2
O ref
F CH
4 0 .
036
CH
4
CH
4
ref
N
2
O ref
f
(
M
,
N
)
CH
4
ref
f
(
M
,
N
) where
CO 2ref
= 383ppmv,
N 2 O ref
= 319ppbv,
CH 4ref
= 1774ppbv • Assumes relatively minor marginal changes in GHG concentrations • Spectral overlap between N 2 O and CH 4 is accounted for • Radiative forcing not related to GHGs (e.g. albedo change) is not considered (IPCC 1997, 2001, 2007)
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 Woody Biomass System
Woody biomass is used for heat and power production, wood frame in building construction Forest strategy: harvest biomass
Forest land Reference Fossil System
Forest strategy: carbon storage
Forest land
Fossil coal is used for heat and power production, concrete frame in building construction 1) Conventional management with 109-year rotation 2) Fertilized management with 69-year rotation 3) Unmanaged and non-harvested management with 20 % increase (3a) and with 20 % decrease (3b)
The same energy and housing service from both of the systems CRF is calculated based on difference in annual GHG emissions between systems
Forest biomass replace concrete constructions – An apartment building example
Case-study building: Wood frame Reference building: Reinforced-concrete frame Built in Växjö, Sweden Hypothetical building with identical size and function 4 stories, 16 apartments, 1190 usable m 2
CO
2
balance of building production and of end-life
• Fossil CO 2 emission from primary energy use for production and distribution of building materials and for assembly and demolition of buildings • CO 2 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
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 CO 2 at a negative exponential rate •Decay constants of: -0.033 for small-diameter logs -0.046 for stumps and coarse roots -0.074 for branches and tops -0.129 for fine roots -0.170 for needles (Næsset 1999) (Melin et al. 2009) (Palviainen et al. 2004) (Palviainen et al. 2004) (Palviainen et al. 2004) Several uncertainties
Stand level living tree biomass stock for the different forest management regimes
350 300 250 200 150 100 50 0 0 Conventional Fertilized Unmanaged (low) Unmanaged (high) 20 40 60 80 100 120
Time (Years)
140 160 180 200 220 240 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
0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 -22 0 Conventional management Fertilized management 20 40 60 80 100 120 140 160 180 200 220 240 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).
.
Stand level CRF for conventional and fertilized forest management – The black line with excluded forest land-use in reference system
0 -2 -14 -16 -18 -20 -22 -4 -6 -8 -10 -12 0 20 40 60 Conventional management Fertilized management 80 100 120 140 160 180 200 220 240 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).
.
Primary energy use in Sweden 2010
TWh
Oil and oil products 190 Narural gas (18) Coal and coke 26
Biofuel, peat, etc.
Pumped heat (5) Hydro power 135 68 Nuclear power Wind power (4) 166 35% Heat plants 12% Electricity production* Other sectors 37% Pulp and paper industry 13% Residential, service, etc.
*
in both industry and district heating sectors
Source: Energy in Sweden 2012, Swedish Energy Agency
Annual Swedish bioenergy use
160 140 120 100 80 60 40 20 0 1980 1985 1990 1995
Year
2000 2005 Source: Swedish Energy Agency: Energy in Sweden 2009, and Kortsiktsprognos 2010 2010
Standing stem volume on Swedish productive forest land and scenarios for 2010 - 2110
5000 4000 3000 2000 1000 Environmental scenario Production scenario Reference scenario Historic data 0 1950 1970 1990 2010 2030 Year 2050 2070 2090 2110 Source: Skogsstyrelsen, Skogliga konsekvensanalyser och virkesbalanser 2008
Conclusions/discussion
• 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
• • • • 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