From Academic Kids
Biofuel is any fuel that derives from biomass - recently living organisms or their metabolic byproducts, such as manure from cows. It is a renewable energy, unlike other natural resources such as petroleum, coal and nuclear fuels. The carbon in biofuels was recently extracted from atmospheric carbon dioxide by growing plants, so burning it does not result in a net increase of carbon dioxide in the Earth's atmosphere. As a result, biofuels are seen by many as a way to reduce the amount of carbon dioxide released into the atmosphere by using them to replace non renewable sources of energy.
Both agricultural products specifically grown for use as biofuels and waste from industry, agriculture, forestry, and households -including straw, lumber, manure, and food leftovers-can be used for the production of bioenergy. Currently, most biofuel is burned to release its stored chemical energy. Research into more efficient methods (http://www.aboutbioenergy.info/technologies.html) of converting biofuels and other fuels into electricity utilizing fuel cells is an area of very active work. Bioenergy covers about 15% of the world's energy consumption. Sweden and Finland supply 17% and 19% respectively, of their energy needs with bioenergy. Biomass can be used both for centralized production of electricity and district heat, and for local heating.
Classes of Biofuels
There are many forms of solid biomass that are combustible as a fuel1 such as:
- Wood — see wood fuel
- straw and other dried plants
- animal waste such as poultry droppings or cattle dung.
- husks or shells from crops such as rice, peanut and cotton.
Dried compressed peat is also sometimes considered a biofuel. However it does not meet the criteria of being a renewable form of energy, or of the carbon being recently absorbed from atmospheric carbon dioxide by growing plants. In the time scales of human industrialisation it is a fossil fuel and burning it does contribute to atmospheric C02.
There are also a number of liquid forms of biomass that can be used as a fuel:
- Bioalcohols — see alcohol as a fuel.
- Ethanol produced from sugar cane is being used as automotive fuel in Brazil. Ethanol produced from corn is being used as a gasoline additive (oxygenator) in the United States.
- Methanol, which is currently produced from natural gas, can also be produced from biomass — although this is not economically viable at present. The methanol economy is an interesting alternative to the hydrogen economy.
- Biologically produced oils can be used in diesel engines:
- Oils and gases can be produced from various wastes:
- Methane produced by the natural decay of garbage or agricultural manure can be collected for use as fuel.
- Hydrogen can be produced by cracking any hydrocarbon fuel in a reformer or by the electrolysis of water.
Energy content of Biofuel
|fuel type||Specific Energy Density (J/kg)||Volumetric Energy Density (J/l)|
|wood fuel||16 נ106 - 21 נ106|
|ethanol||23.4 נ106 - 26.8 נ106|
|methanol||19.9 נ106 - 22.7 נ106|
|Methane||55 נ106 - 55.7 נ106|
|Hydrogen||120 נ106 - 142 נ106|
Biofuels have a low specific energy density compared to fossil fuels. This means that biomass energy schemes must work at a local level as their success depends on well-structured and sustainable fuel supply networks from local producers.
Small scale use of biofuels
A widespread use of biofuels is in home cooking and heating. Typical fuels for this are wood, charcoal or dried dung. The biofuel may be burned on an open fireplace or in a special stove. The efficiency of this process may vary widely from 10% for a well made fire up (even less if the fire is not made carefully) to 40% for a custom designed charcoal stove1. Inefficient use of fuel may be a minor cause of deforestation (though this is negligible compared to deliberate destruction to clear land for agricultural use) but more importantly it means that more work has to be put into gathering fuel, thus the quality of cooking stoves has a direct influence on the viability of biofuels.
Unfortunately, much cooking with biofuels is done indoors, without efficient ventilation and using those fuels such as dung which cause most airborne polution. This can be a serious health hazard; 1.5 million deaths were attributed to this cause by the World Health Organisation in 20002. There are various responses to this, such as improved stoves, including those with inbuilt flues and switching to alternative fuel sources. Most of these responses have difficulties, for example flues are expensive and easily damage; alternative fuels tend to be more expensive which is difficult to implement since the people who rely on biofuels often do so precisely because they cannot afford alternatives.3 Organisations such as Intermediate Technology Development Group work to make improved facilities for biofuel use and better alternatives accessible to those who cannot currently get them. This work be done through designing improved ventilation, a switch to different usage of biomass such as through the creation of biogas from solid biomatter or a switch to other alternatives such as micro-hydro power.
Implementation of biofuels use on the national level
On the other hand, recognizing the importance of bioenergy and it's implementation, there are international organisations such as IEA Bioenergy (http://www.ieabioenergy.com/IEABioenergy.php), which was established in 1978 by the International Energy Agency (IEA), with the aim of improving cooperation and information exchange between countries that have national programmes in bioenergy research, development and deployment.