4/4/2013 Sustainable energy sources Biomass Incident solar energy = 178,000 Twatts = 15,000 times global energy demand 6 CO + 6 H O + energy ? C H O + 6O XXXXXXXXXX Photosynthetic efficiency = 11%, theoretical Plants fix 2E11 tons CO2/year and store = 3 –6%, actual 70E3 MTEP, which is 10 times global energy needs. Sustainable energy sources Biomass to Bioenergy Biomass for bioenergy production: - Wood US biomass energy consumption, - Agricultural crops 2010 - Crop wastes - Animal wastes - Solid wastes Technologies for conversion of biomass to bioenergy: - Combustion to heat/electricity - Fermentation to fuels - Anaerobic digestion to biogas - Chemical conversion to fuels 14/4/2013 Sustainable energy sources Biomass to Bioenergy Direct combustion- Cooking, heating, steam-to-electricity (Rankine cycle) Thermochemical conversion- Heating at 5 atm. without O to produce CO + H (“syngas”) 2 2 for further conversion to ethanol or hydrogen Biochemical conversion- 1) Fermentation to produce alcohols, ethanol 2) Anaerobic digestion to produce CO + CH (“biogas”) 2 4 3) Anaerobic digestion to produce CO + H (“biohydrogen”) 2 2 Transesterification- Conversion of bio-oils (“triglycerides”) to methyl or ethyl esters of fatty acids (“biodiesel”) Sustainable energy sources Biomass to Bioenergy First generation of biofuels -Use of food crops (corn, sugar beet, oil seeds etc) -mature technology, drop-in fuel Second generation of biofuels -Use of non-food (straw, bagasse, crop wastes etc) -near-mature technology, drop-in fuel Third generation of biofuels -Algal biodiesel -emerging technology Fourth generation of biofuels -Genetically modified crops, advanced bioconversion processes, energy-efficient cultivation/processing 24/4/2013 Sustainable energy sources Biofuel pathways Sustainable energy sources Biofuel pathways 3