Carbon footprint of electricity production from an innovative biogas system with steam explosion pretreatment

Transcription

1 Carbon footprint of electricity production from an innovative biogas system with steam explosion pretreatment Case study of a 500-kW Austrian biogas facility Iris Kral 1

2 Motivation l 2

3 Motivation ll Maize silage Biogas Digester Agricultural residues 3

4 Input substrates in biogas production Maize Silage Scenario Maize Stover Scenario Including pretreatment Seilnacht, 2014 Uidl,

5 Steam Explosion Pretreatment of biomass - high temperature, saturated steam ( C) for 5 20 min - rapid pressure drop easily digestible input material for anaerobic digestion 5

6 What is environmental life-cycle assessment (LCA)? LCA adds all emissions and resource use (e.g. diesel use and CO 2 emissions) from manufacturing to disposal LCA calculates their environmental impacts LCA works for products and production systems at different scales 6

7 Biogas plant and CHP settings Main components: concrete, asphalt, crushed rocks, steel, iron Rated power of the CHP unit: 500 kw el Electrical efficiency: 38% 50% off-heat usage GE Jenbacher, 2014 Bioferm,

8 LCA model Functional unit: 1 kwh electrical energy at the CHP unit Modelling software: Open LCA v.1.4 Data: Primary data from CHP manufacturer; Secondary data from Ecoinvent 2.2 database and literature Uncertainty analysis: Monte Carlo simulations Impact assesment methods ReCiPe midpoint and CED 8

9 System diagram Maize silage scenario Maize stover scenario System boundary System boundary Output: 3,735,000 kwh/a electricity and 1,994,490 kwh/a heat 9

10 System boundary Used heat 10

11 Maize silage scenario Maize stover scenario System boundary System boundary 11

12 System boundary 12

13 Results 13

14 Global warming potential 100yr time horizon Maize silage scenario Maize stover scenario 287 g CO 2 -eq/kwhel 239 g CO 2 -eq/kwhel Seilnacht, 2014 Uidl,

15 GWP of contributing processes stover scenario in kg CO 2 -eq and percent 15

16 GWP of contributing processes (both scenarios) kg CO 2 -eq per kwh el Substrate: Silage Substrate: Maize stover CHP (methane slip) Electricity for plant operations Construction materials Fermenter leaks Maintenance 16

17 Relative impact Other impact categories 100% 80% 60% 40% 20% 0% Climate change Freshwater ecotoxicity Human toxicity Particulate matter formation Terrestrial acidification Non-renewable energy demand Renewable energy demand SIL Scenario STO Scenario 17

18 Conclusions The main contribution to GHG emissions from electricity production from biogas comes from unburned methane emitted at the CHP unit. The additional emissions caused by the construction and operation of the SE pretreatment unit are of minor importance (0.5 g CO 2 -eq/kwh). The use of agricultural residues as biogas substrates after pretreatment can be a suitable alternative to the use of energy crops. 18

19 Thank you for your attention Project team: Iris Kral, Gerhard Piringer, Molly Saylor, Andreas Gronauer and Alexander Bauer 19