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