Description and Purpose
Biofuel is dead plant or (sometimes) animal matter processed into a more efficient or convenient fuel. Biofuels are produced either from waste, such as plant trimmings, wood, or from deliberately cultivated crops, such as corn (below). The most common end products are ethanol, vegetable oil, and what can be called mixed refuse.
Biofuels are meant to be an economical and sustainable substitute for fossil fuels. As compared to petroleum, for example, solar cells and nuclear power are completely different technologies. The right liquid biofuel, though, can be used in combustion engines in place of petroleum products with little or no modifications. Similarly, coal as a fuel source can be replaced with an appropriate solid biofuel.
Additionally, the right biofuels pollute less than fossil fuels they replace. Biofuels reclaimed from waste also reduce landfill and other garbage disposal problems. To some extent, these two benefits are a tradeoff, for reclaimed biowaste tends to burn dirtier than fuels grown for the job.
Kinds of Biofuel
One of the most common biofuels is ethanol, ethyl alcohol. Ethanol is a liquid fuel with about 65% of the energy content of gasoline by volume. It can be added to gasoline in small amounts and used in automobile engines with only minor modifications. Pure ethanol is a viable fuel in areas where gasoline is expensive or ethanol manufacture is cheap. Brazil uses large amounts of ethanol as an automobile fuel in engines that are suitably designed.
Ethanol manufacture is a variation on the ancient craft of fermentation. Yeast converts glucose sugar from plants such as sugar cane to alcohol. Since starch is just a string of glucose molecules, starch from corn or other sources can also be converted to ethanol. Extracting and purifying the ethanol requires distillation, which requires heat. This is a major cost at the moment – producing energy requires energy.
A variety of vegetable oils are used as biofuels. Peanut oil is one choice; canola oil is another. These vegetable oils can be extracted from plants grown for the purpose, or they can be waste cooking oil from restaurants and food processing industries. Waste oil must be filtered before use.
Biofuel vegetable oils have two common uses. They can be burned in furnaces for heating or industrial applications. They are also suitable for diesel truck engines with slight retrofitting. (Vehicles running on peanut oil have a distinctive smell.) One administrative obstacle to using vegetable oils for this purpose is that gasoline taxes fund roads in many jurisdictions. Vegetable oil as fuel can be seen as circumventing the tax, and it may be illegal or taxed out of the realm of profitability.
Solid biofuels are yet another category. Solids tend to be mixtures of wood chips, lawn cuttings, and other combustible waste. Such waste is normally dried, mixed, and formed into relatively uniform pellets for burning. These pellets likely still contain dirt, trace toxins, and other problematic contaminants, limiting their use. Furnaces that use pellet fuel should be well vented or scrub their emissions of pollution, or both.