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Biomass and Biofuels

Biomass and Biofuels. MECH 5970 25 April 2011. Background. Biomass: material of recent biological origin. Provides (directly or via processing) HC fuel for combustion applications. Very long history Wine, beer making: fermentation methods Wood (a biofuel ) was the original fuel.

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Biomass and Biofuels

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  1. Biomass and Biofuels MECH 5970 25 April 2011

  2. Background • Biomass: material of recent biological origin. • Provides (directly or via processing) HC fuel for combustion applications. • Very long history • Wine, beer making: fermentation methods • Wood (a biofuel) was the original fuel. • Whaling: provided the original lamp oil.

  3. Current status

  4. 2005-2008: ethanol is gasoline increased from 3.8 to 5.5%, and biodiesel in diesel increased from 0.9 to 1.5%

  5. Critical issues • Competition of resources: • Water • Agricultural land • Agricultural products: food vs. fuel. • Effect of extensive energy crop farming on ecosystem and climate. • Net energy return: are fossil fuels saved? • CO2 neutrality of biofuels is not always obvious.

  6. Types of biofuels • Plant oil based (sunflower, palm, waste oil,…) • Straight use of oil with minor modifications (water removal, viscosity reduction) in diesel cycles. • Biodiesel: transesterfication of plant oil to provide fatty acid methyl ester (FAME). • “Green diesel”: traditional fractional distillation of plant oil.

  7. Alcohol based fuels • Ethanol from agricultural crops (carbohydrate feed stock): corn, cereals, sugar cane, beets, cassava,… • Fermentation to ethanol/water mix. • Distillation to ethanol.

  8. Alcohol based fuels • Ethanol from herbaceous and woody crops (cellulosic biomass): grasses, corn stover, wood,… • Breakdown (digestion) of cellulosic biomass in several steps to form sugars. • Fermentation of sugars to ethanol/water mix. • Distillation to ethanol. • Methanol: chemical, rather than biochemical, process.

  9. Gas fuels • Biogas: primarily CH4, CO2 • Produced by anerobic digestion and/or fermentation of biodegradable materials. • Swamp gas, landfill gas. • Syngas: H2 and CO • Produced by partial oxidation (pyrolosis) of biomass.

  10. Cellulosic ethanol • Biological approach: • Cellulose hydrolysis: pretreatment and digestion of cellulose into sugars • Fermentation to ethanol, followed by distillation, purification • Thermochemical approach: • Partial oxidation of cellulose to CO, CO2, H2 • Fermentation using Clostridium ljungdahlii to ethanol

  11. Algae—based fuels • Advantages over crop—based fuels: • Better use of water resources (can use salt, waste water) • Theoretically yield 10-100 times more energy per unit area than croplands. • Simplified process: algae consume CO2, produce fuel (oils or alcohols).

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