B6d Summary

B6d Summary

What are biofuels?
1. produced by burning biomass
  1. e.g. wood, alcohol, biogas
2. BIOMASS
  1. photosynthesis produces biomass in plants
    1. cardon dioxide + water --> glucose + oxygen
  2. how is energy transferred?
    1. fast growing trees can be burnt
      1. releasing heat
    2. biomass can be fermented by yeast & bacteria
      1. to create products e.g. biogas
        can be used as fuels
3. BIOGAS
  1. Contains...
    1. 70% methane (CH4)
    2. 30% carbon dioxide (CO2)
    3. also contains traces of...
      1. hydrogen
      2. nitrogen
      3. hydrogen sulfide
    4. biogas containing >50% methane burns easily
      1. but around 10% methane is eplosive
  2. displaces air & reduces O2 levels
    1. restricting respiration
    2. so keep well ventilated
    3. higher risk of explosion
  3. if there are explosions landfill sites
    1. may be unusable for many years
  4. production is fastest at 32-35°C
    1. because fermenting bacteria grow best at this temp.
4. Gasohol
  1. mixture of ethanol (10%) and petrol (90%)
  2. most economically viable in places
    1. where there is plenty of sugar cane & not a lot of oil
      1. ethanol produced by fermentation of glucose by yeast
        sugar cane works as a source of glucose
Advantages
1. RENEWABLE
  1. crops which are decomposed to make biogas
    1. quickly replaced with new plants
2. CARBON NEUTRAL
  1. plants grown to make biogas photosynthesise
    1. removing CO2 from the atmosphere
  2. balancing out the release of CO2
    1. from burning the biofuel
  3. but the biofuel has to be burnt at the same rate
    1. as new biomass is produced
3. of biogas
  1. reduces fossil fuel consumption
  2. produces no particulates when burnt
  3. no overall increase in levels
    1. of greenhouse gases
Disadvantages
1. of biogas
  1. doesn't contain as much energy
    1. as same volume of natural gas
    2. because it is more dilute
      1. natural gas has as much higher % of CH4
  2. can lead to habitat loss
    1. and so extinction of species
2. large areas of land sometimes cleared of vegetation
  1. to create space to produce biofuels
    1. causes extinction of species due to habitat loss
      1. and change in food availability

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