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Co-digestion of manure with straw and perennial grasses

Co-digestion of manure with straw and perennial grasses. Henrik Bjarne Møller, Department of Engineering, Aarhus University, Denmark. Straw and perennial grass for biogas. Why use straw and perennial grass?

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Co-digestion of manure with straw and perennial grasses

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  1. Co-digestion of manure with straw and perennial grasses Henrik Bjarne Møller, Department of Engineering, Aarhus University, Denmark

  2. Straw and perennialgrass for biogas • Why use straw and perennial grass? • Biogas plants miss high value substrates for biogas production as co-substrates for livestock manure - crops should be phased out. • Straw is the agricultural by-product with the highest energy potential. • Recycle nutrients from uncultivated meadows to organic arable land. • Harvest of meadows has a number of positive side effects • What conditions must be met? • There must be a positive economy and in the short term the economy must be in line with corn. • Biogas technology should be optimized to handled and convert the biomass

  3. Biogas research plant Fullscale plant • 1,200 m3 digester, • 22,000 tonnesmanure) • 4,100 tonnes straw , Grass and maize Solid feeding >1.7 mill. m3 biogas 3,223 MWh el 6,200 MWh heat Fullscale pre-treatment • Extruder • Briquetting Gas upgrading • Research plant • 2 x 30m3 CSTR pilot digesters • 2 x 10m3 CSTR pilot • digesters

  4. Handling and pre-treatment of grass/straw at Foulum Wet-line (20-80% DM) Dry-line (>80% DM) Digestion Pre-treatment Storage Feeding

  5. Transition from maize to fiber richmaterial In warmperiods dosing of solid material is reduceddue to lack of gas sale

  6. Biomass – Foulum biogas plant

  7. Pre-treatment of ligno-cellulose - why? hemicellulose • Improvement • Loweringofviscosityandmixingability • Higher methaneyield cellulose Lignin • Drawbacks • Higher energydemand • Investment andrunningcosts

  8. Types of pre-treatment of ligno-cellulose - why? Untreated Macerated Briquetting Extrudation

  9. Gas potentials of straw/grass – effect of briqueting/extrudation

  10. Gas potentials – effect of briqueting and chemicals

  11. Pre-treatment – Energy demand Energy consumption

  12. Energy balances by pre-treatment

  13. Economy

  14. Economy

  15. Experiments with co-digestion of straw Volume: 15 L Temperature: 49±1 oC Stirring: 100 rpm HRT: 20 days 30 m3 Temperature: 50 oC HRT: 25 days Briqueting of straw

  16. Thermophilic co-digestion of strawinfluence of sulfur in gas Addition of 8,3% wheatstrawreducesulphur to 25% of original

  17. Co-digestion of strawinfluence of hydraulic retention time Thermophilic Thermophilic/mesophilic + 30% + 30% If retention time shouldbeprolongedmesophilicconditions is sufficient

  18. Foulum biogas plant – primary and post digestion Thermophilic Thermophilic/mesophilic 0,5-5 m3/ton + 37% Thermophilic 53oC HRT=13 days Mesophilic 25- 30oC HRT=40 days Psycrophilic 0-20oC HRT=100 days Psycrophilic 10-20oC HRT=40 days

  19. Conclusion • Strawcansuccesfullybeused for co-digestion of straw and manure, pre-treatmentcanenhance the yield. • The increasedyielddepends on technology and retention time in the biogasplant. • With short retention time, post digestion is recomended • Mechanical and chemicalpre-treatmentcanbecombined with briquettingtechnology • Foulum biogas plant has beenthrough a succesfull transition • from highvalueenergycrops to straw • Strawreducessulphur in the gas significantly

  20. Thanks for your attention

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