Alternative Fuels Essay Research Paper Alternative Fuel — страница 2

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To learn more about hydrogen go to the Hydrogen Fuel Page. Vehicle AvailabilityThere are no vehicles currently available that use hydrogen as a fuel; however, automobile manufacturers have experimented with developing vehicles that use hydrogen. Research vehicles have been produced by Daimler-Benz, BMW and Mazda. The Mercedes-Benz and BMW vehicles use liquid hydrogen. The Mazda vehicle stores its hydrogen as a gas in a metal-hydride lattice of shaved metal. Other vehicles have been built using compressed hydrogen, including two vehicles in Arizona operated by the American Hydrogen Association. High production costs and low density have prevented hydrogen’s use as a transportation fuel in all but test programs. It may be 20 to 30 years or more before hydrogen is a viable

transportation fuel and then perhaps only in fuel-cell-powered vehicles.What is Ethanol?Ethanol (ethyl alcohol, grain alcohol, ETOH) is a clear, colorless liquid with a characteristic, agreeable odor. In dilute aqueous solution, it has a somewhat sweet flavor, but in more concentrated solutions it has a burning taste. Ethanol, CH4CH3OH, is an alcohol, a group of chemical compounds whose molecules contain a hydroxyl group, -OH, bonded to a carbon atom. Two higher blends of ethanol, E-85 and E-95 are being explored as alternative fuels in demonstration programs. Ethanol is also made into an ether, ethyltertiary-butyl ether (ETBE), that has properties of interest for oxygenated gasoline and reformulated fuels. Chemical Properties: Ethanol is ethane with a hydrogen molecule replaced

by a hydroxyl radical. See the fuel properties table (PDF: 116 KB) for more information. How is Ethanol Made?There are basically eight steps in the ethanol production process: 1. Milling: The corn (or barley or wheat) will first pass through hammer mills, which grind it into a fine powder called meal. 2. Liquefaction: The meal will then be mixed with water and alpha-amylase, and will pass through cookers where the starch is liquefied. Heat will be applied at this stage to enable liquefaction. Cookers with a high temperature stage (120-150 degrees Celsius) and a lower Temperature-holding period (95 degrees Celsius) will be used. These high temperatures reduce bacteria levels in the mash. 3. Saccharification: The mash from the cookers will then be cooled and the secondary enzyme

(gluco-amylase) will be added to convert the liquefied starch to fermentable sugars (dextrose), a process called saccharification. 4. Fermentation: Yeast will then be added to the mash to ferment the sugars to ethanol and carbon dioxide. Using a continuous process, the fermenting mash will be allowed to flow, or cascade, through several fermenters until the mash is fully fermented and then leaves the final tank. In a batch fermentation process, the mash stays in one fermenter for about 48 hours before the distillation process is started. 5. Distillation: The fermented mash, now called “beer,” will contain about 10% alcohol, as well as all the non-fermentable solids from the corn and the yeast cells. The mash will then be pumped to the continuous flow, multi-column

distillation system where the alcohol will be removed from the solids and the water. The alcohol will leave the top of the final column at about 96% strength, and the residue mash, called stillage, will be transferred from the base of the column to the co-product processing area. 6. Dehydration: The alcohol from the top of the column will then pass through a dehydration system where the remaining water will be removed. Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol. The alcohol product at this stage is called anhydrous (pure, without water) ethanol and is approximately 200 proof. 7. Denaturing: Ethanol that will be used for fuel is then denatured with a small amount (2-5%) of some product, like gasoline, to make it unfit for human

consumption. 8. Co-Products: There are two main co-products created in the production of ethanol: carbon dioxide and distillers grain. Carbon dioxide is given off in great quantities during fermentation and many ethanol plants collect that carbon dioxide, clean it of any residual alcohol, compress it and sell it for use to carbonate beverages or in the flash freezing of meat. Distillers grains, wet and dried, are high in protein and other nutrients and are a highly valued livestock feed ingredient. Some ethanol plants also create a “syrup” containing some of the solids that can be a separate production sold in addition to the distiller’s grain, or combined with it. Ethanol production is a no-waste process that adds value to the corn by converting it into more valuable