Biofuel
The definition of biofuel is liquid or gas transportation fuel derived from biomass.
Plants use photosynthesis to grow and produce biomass. Also known as biomatter, biomass can be used directly as fuel or to produce liquid biofuel. Agriculturally produced biomass fuels, such as biodiesel, ethanol and bagasse (often a by-product of sugar cane cultivation) can be burned in internal combustion engines or boilers. Typically biofuel is burned to release its stored chemical energy. Research into more efficient methods of converting biofuels and other fuels into electricity utilizing fuel cells is an area of very active work.
Liquid biofuel
Liquid biofuel is usually either a bioalcohol such as ethanol or a bio-oil such as biodiesel and straight vegetable oil. Biodiesel can be used in modern diesel vehicles with little or no modification to the engine and can be made from waste and virgin vegetable and animal oil and fats (lipids). Virgin vegetable oils can be used in modified diesel engines. In fact the Diesel engine was originally designed to run on vegetable oil rather than fossil fuel. A major benefit of biodiesel is lower emissions. The use of biodiesel reduces emission of carbon monoxide and other hydrocarbons by 20 to 40%. In some areas corn, cornstalks, sugarbeets, sugar cane, and switchgrasses are grown specifically to produce ethanol (also known as grain alcohol) a liquid which can be used in internal combustion engines and fuel cells. Ethanol is being phased into the current energy infrastructure. E85 is a fuel composed of 85% ethanol and 15% gasoline that is sold to consumers. Biobutanol is being developed as an alternative to bioethanol.
Information on pump, California.
In the future, there might be bio-synthetic liquid fuel available. It can be produced by the Fischer-Tropsch process, also called Biomass-To-Liquids (BTL).
Solid biomass
Direct use is usually in the form of combustible solids, either wood, the biogenic portion of municipal solid waste or combustible field crops. Field crops may be grown specifically for combustion or may be used for other purposes, and the processed plant waste then used for combustion. Most sorts of biomatter, including dried manure, can actually be burnt to heat water and to drive turbines.
Sugar cane residue, wheat chaff, corn cobs and other plant matter can be, and are, burned quite successfully. The net carbon dioxide emissions that are added to the atmosphere by this process are only from the fossil fuel that is often currently consumed to plant, fertilize, harvest and transport the biomass.
Sugar cane residue can be used as a biofuel
Processes to harvest biomass from short-rotation poplars and willows, and perennial grasses such as switchgrass, phalaris, and miscanthus, require less frequent cultivation and less nitrogen than from typical annual crops. Pelletizing miscanthus and co-firing it with coal for generating electricity is being studied and may be economically viable. The higher heating value of cellulose is about 17.4 MJ/kg . The estimated yield of ethanol from dry cellulose is about 0.2 kg of ethanol per kg of cellulose (60 gal/ton). Since the higher heating value of ethanol is 29.7 MJ/kg of ethanol it would be 5.94 MJ/kg of the cellulose that it is made from. Thus the ethanol contains only about 1/3 as much energy as the cellulose that it was made from. Co-firing cellulose with coal would replace about three times as much fossil fuel as using the cellulose to make ethanol. The replaced coal would produce 0.0946 kg COâ‚‚/MJ while the replaced liquid fuel would produce only about 0.0733 kg COâ‚‚/MJ so co-firing the cellulose with coal is about 3.8 times more effective at reducing COâ‚‚ emissions than using it to make ethanol.
Solid biomass can also be gasified, and used as described in the next section.
Biogas
Biogas can easily be produced from current waste streams, such as: paper production, sugar production, sewage, animal waste and so forth. These various waste streams have to be slurried together and allowed to naturally ferment, producing methane gas. This can be done by converting current sewage plants into biogas plants. When a biogas plant has extracted all the methane it can, the remains are sometimes better suitable as fertilizer than the original biomass.
Alternatively biogas can be produced via advanced waste processing systems such as mechanical biological treatment. These systems recover the recyclable elements of household waste and process the biodegradable fraction in anaerobic digesters.
Renewable natural gas is a biogas which has been upgraded to a quality similar to natural gas. By upgrading the quality to that of natural gas, it becomes possible to distribute the gas to the mass market via gas grid.
Source:http://en.wikipedia.org