Grass and grass-legume biomass as biogas substrate

Transcription

1 Thomas Prade Department of Biosystems and Technology Grass and grass-legume biomass as biogas substrate Environmental and economic sustainability at different cultivation intensities Thomas Prade IBBA workshop, Esbjerg, Denmark, 25 August 2016

2 Grass in crop rotations Binds carbon in the soil which leads to improved cultivating properties (yield level, nitrogen efficiency, soil structure) Pre-crop effect What are the environmental and economic effects of intensive grass cultivation?

3 Regions Focus Cereal share Grass share Cereal production High Low Livestock production Low High C2 L C1 Björnsson, L., Prade, T., and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden. Illustrationer: Anna Persson.

4 How much can grass contribute? wheat oat wheat wheat barley oat soil carbon effect [kg/ha] without with oat grass I grass II grass III soil carbon effect without with C L wheat s.beet barley wheat barley rapeseed soil carbon effect without with -35 C Björnsson, L., Prade, T., and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden. Illustrationer: Anna Persson.

5 Grass as a biogas substrate Björnsson, L., Prade, T.,and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden. Illustrationer: Anna Persson.

6 Economic effects Soil organic carbon * higher N-efficiency * better soil structure * lower risk for soil compaction Reduction of greenhouse gas emissions Revenues from sale as biogas substrate Benefit for the farmer Climate benefit Should cover the costs Björnsson, L., Prade, T., and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden.

7 Economic result L region Costs and revenues [ /ha] current modified Livestock Cultivation Harvest Storage Transport Oat Grass Internal feed costs assumed unchanged A reasonable price for biogas substrate is 1 kr/kg (~110 /t) The economic result was improved! Costs [ /t DM] Market price of vehicle fuel Capital Other Raw material L Process energy Distribution Björnsson, L., Prade, T., and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden.

8 Economic result C regions Costs and revenues [kr/ha] current modified current modified Cereal 1 Cereal 2 Cultivation Harvest Storage Transport Winter wheat Sugarbeet Spring barley Winter rapeseed Oat Costs [ /t DM] C1 Capital Other Raw material Björnsson, L., Prade, T., and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden. An unchanged economic result was assumed The minimum price for grass as biogas substrate was calculated Market price for vehicle fuel C2 Process energy Distribution

9 GHG emissions ISO-LCA 2,0 Digestate spread. GHG emissions [t CO 2 -eq per hectare and year] 1,5 1,0 0,5 0,0 Digestate spreading -0,5-1,0 Cultivation inputs Field emissions Cultivation inputs Field emissions Cultivation inputs Field emissions Cultivation inputs Field_emissions C1 current C1 modified C2 current C2 modified Mineral fertilizer & material Diesel & energy input Nitrous oxide from mineral fertilizer Nitrous oxide from digestate Nitrous oxide from crop residues Nitrous oxide indirect Soil organic carbon Björnsson, L., Prade, T., and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden.

10 GHG emissions field-to-fuel Field-to-fuel GHG emission reductions in the modified crop rotation compared to current crop rotation: C kg/ha/a CO 2 -equivalents C kg/ha/a CO 2 -equivalents Carbon source/sink ISO LCA EU-RED Electricity mix Soil carbon - Land use change - Digestate use - Crop residues N 2 O emissions - Direct (crop residues, mineral N, bio NH 4 -N, org-n) - Indirect (N-leakage, NH 3 -N) Swedish (11 kg CO 2 -eq/gj) Nordic (35 kg CO 2 -eq/gj) - Residues are excluded - EC (2009) Directive on the promotion of the use of energy from renewable sources (2009/28/EC). Council of the European Union, Brussels, Belgium, 47 pp

11 GHG emissions field-to-fuel Max GHG emissions for 60% reduction: 33,6 g/mj Björnsson, L., Prade, T., and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden.

12 GHG emissions field-to-fuel Max GHG emissions for 60% reduction: 33,6 g/mj Björnsson, L., Prade, T., and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden.

13 GHG emissions field-to-fuel Björnsson, L., Prade, T., and Lantz, M., Grass for biogas - Arable land as carbon sink. An environmental and economic assessment of carbon sequestration in arable land through introduction of grass for biogas production, Energiforsk, Stockholm, Sweden.

14 Summary Intensive grass cultivation contributes to SOC build-up which can turn arable land from GHG source to carbon sink produces biomass for renewable fuels which require some economic support. How much is SOC built-up/ghg mitigation worth?

15 Grass on marginal soils Can we produce sustainable vehicle fuel from extensively managed marginal soils?

16 GHG emissions field-to-fuel GHG emissions [g CO 2 -eq./mj] Marginal fields Recovered biomass DM yield [t/ha] Fossil diesel 60% reduction Mineral N fertilization 120 kg N/ha 100 kg N/ha 60 kg N/ha 0 kg N/ha Carlsson, G., Mårtensson, L.-M., Prade, T., Svensson, S.-E., and Jensen, E.S Perennial species mixtures for multifunctional production of biomass on marginal land. GCB Bioenergy.

17 GHG emissions field-to-fuel Minimum biomass DM yield at 60% GHG emission reduction: Minimum biomass DM yield [t/ha] y = 0,0825x + 0,2083 R² = 0, N-fertilization [kg/ha] A return of ca 80 kg DM biomass per kg N added is required! => N content of 1,25%; grass typically 2,5 %!

18 Economic aspects field-to-fuel Marginal fields Fully fertilized grass (digestate + mineral fertilizer) C1:m C2:m L:m Production cost [ /t] Resonable substrate price Biomass DM yield [t/ha] Carlsson, G., Mårtensson, L.-M., Prade, T., Svensson, S.-E., and Jensen, E.S Perennial species mixtures for multifunctional production of biomass on marginal land. GCB Bioenergy.

19 Economic aspects field-to-fuel 160 Marginal fields Production cost [ /t] PK-fertilized grass C1:m C2:m L:m 60 Unfertilized grass Biomass DM yield [t/ha] Carlsson, G., Mårtensson, L.-M., Prade, T., Svensson, S.-E., and Jensen, E.S Perennial species mixtures for multifunctional production of biomass on marginal land. GCB Bioenergy.

20 Summary Extensive grass cultivation on marginal soils can deliver biogas substrate that fulfills the 60% GHG reduction target for unfertilized grass crops and fertilized when yielding 80 kg/kg N with promising production costs at biomass yields >~6-8 t DM/ha with PK-fertilization >~4 t DM/ha unfertilized (e.g. with N-fixating plants)

21 Conclusions I Grass cultivation is an effective measure for turning the negative SOC trend Grass cultivation is currently not economically viable i cereal regions where it would give the greatest benefits Grass is an economically suitable substrate for co-digestion, where only small technical adaptations are needed

22 Conclusions II GHG mitigation target is barely missed, when excluding SOC effects according EU-RED It is reasonable to reach harvestable biomass yields 4-5 t DM/ha on marginal soils without fertilization, but K removal may reduce yields over time

23 Thomas Prade Department of Biosystems and Technology Thank you! Thomas Prade Swedish University of Agricultural Sciences (SLU) Department of Biosystems and Technology Alnarp, Sweden