APES 6.7 Energy from Biomass

Enduring Understanding:

  • Humans use energy from a variety of sources, resulting in positive and negative consequences.

Learning Objective:

  • Describe the effects of the use of biomass in power generation on the environment.

Essential Knowledge:

  • Burning of biomass produces heat for energy at a relatively low cost, but it also produces carbon dioxide, carbon monoxide, nitrogen oxides, particulates, and volatile organic compounds.  The overharvesting of trees for fuel also causes deforestation.
  • Ethanol can be used as a substitute for gasoline.  Burning ethanol does not introduce additional carbon into the atmosphere via combustion, but the energy return on energy investment for ethanol is low.

Process

  • Biomass stores energy from the sun, from photosynthesis
    • Remember the first law of thermodynamics: Energy cannot be created or destroyed
  • Biomass is the leading renewable energy worldwide
    • Burning biomass is a direct source of heat for many in developing nations
    • Examples of biomass used for heat include:
    • Wood, peat, charcoal, crop residue, and manure
    • In this way, it can be used for heating, cooking fires, light, etc.

Types

Biofuel

  • Biofuels are liquid fuels made from plant matter that can be used as substitutes for conventional petroleum products
  • Ethanol
    • Made by fermenting plant-based starches into sugars and eventually alcohol
    • Typically mixed with gasoline to create ‘gasohol;’ 90% gas and 10% ethanol
    • E-85 and flex-fuel vehicles can run on a mixture of 85% ethanol and 15% gas
    • Switchgrass is being looked into as a better alternative
  • Sources
    • Corn from the US, sugarcane from brazil, and sugar beets from both

Biodiesel

  • Extracted and chemically modified oil from plants
    • Can be a direct substitute for diesel fuel
  • Sources
    • Soybeans from Brazil and the US, oil palms from Southeast Asia, and rapeseed from Europe
  • Using biofuels and biodiesel uses infrastructure that is already in place
  • Straight Vegetable Oil (SVO) and algae could be more sustainable sources

Advantages and Disadvantages

Benefits

  • Combustion in carbon neutral
    • This is modern carbon meaning the carbon was already cycling actively
    • Fossil fuels add carbon dioxide that was not actively cycling
  • Potentially renewable is used sustainably
  • Can be produced domestically

Drawbacks

  • Net energy is low
    • More gasohol is needed to go the same distance
  • Harvesting of crops for ethanol has potential for…
    • Increased use of fossil fuels in harvest
    • Increased deforestation
    • Reduction in fertility of agricultural land

Environmental Consequences

Positive Consequences

  • Easily accessible
  • Relatively inexpensive
  • Can be used for heating and cooking easily
  • Can produce electricity
    • This is, however, a longer process

Negative Consequences

  • Pollutes the air
    • CO2, CO, nitrogen oxides, particulates, and volatile organic compounds
  • Typically burned indoors, intensifying health effects of pollutants
  • Overharvesting of trees for fuelwood and result in deforestation