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Energy Resources - Concept 3 Renewable energy sources.

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Introduction

Energy Resources - Concept 3 Renewable energy sources Energy from Biomass Traditionally, wood is the main form in which biomass is used as an energy source. The biomass is used to boil water to provide steam to turn turbines. In Great Britain most commercially produced wood is used for timber, but when a conifer plantation is felled, there are branches and low-grade timber that can be used for fuel. Straw left over from harvesting cereal crops can also be used to produce energy. When used for energy the cost of collecting, storage and transporting bulky problems is a problem. Most examples rely on a community-based collection used locally in a close plant or used on the farm that produced the straw and is widely used in Denmark and the USA. Stubble used to be burnt, but this was made illegal in the UK. Most stubble is used for bedding. When burnt straw leaves ash, which contains nutrients, which can quickly be extracted from the soil by the new crop. This method is still used in many developing countries. It is very rarely ploughed in as it takes along time to biodegrade and as it does so it creates anaerobic pockets in the soil. ...read more.

Middle

Ethanol is a much cleaner fuel and produces much less pollution, but it is much more expensive to produce. Especially as the farmers can also sell the crop to be made into refined sugar. This production is unlikely ever to work due to politics and the oil industry. In the end it can not be considered as a real alternative ,as 80-90% of it is made from a fossil fuel. Once the sugar is extracted the fibrous residue (bagasse) is dried and then burnt as a fuel to ferment the malasses. 1) Growing and cropping of sugar. 2) Extraction of sugars by crushing and washing cane. 3) Crystallization out of sucrose (for sale) leaving the syrup of glucose and fructose (molases) 4) Fermentation of molasses to yield dilute alcohol. 5) Distillation of dilute alcohol to give pure ethanol, using bagasse as a power source. A more promising is oilseed rape which has been used to power buses in certain areas of the UK as part of a trial and in Italy, it is added to diesel and can be added to make up 30% of the mixture (rpae methyl ester, RME). It produces fewer sooty particles and no sulphur dioxide. ...read more.

Conclusion

The digestion process occurs in 3 stages: 1) Aerobic bacteria convert lipids and carbohydrates in the biomass into sugars, fatty acids, amino acids and glycerol by hydrolysis (0-10 days, acids cause pH to fall). 2) Acetogenic bacteria convert sugars and other products of stage 1 into short-chain fatty acids e.g. acetic acid = acetogenesis (stages 2+3, 10-45 days acids used up, pH increases, methane produced.). 3) Anaerobic bacteria convert the fatty acids into methane = methogenesis. Conditions must be anaerobic as the bacteria are only active when there is no oxygen present. They are called obligate anaerobes. Temperatures must be kept between 30-40o because the bacteria are sensitive to temperature changes. The reactions take place in a digester. It must be i) Strong and large enough to hold large volumes of liquid and withstand pressure build up. ii) Gas-tight and allow aerobic conditions to be maintained. iii) Have an inlet for loading material, an outlet for the gas and a way of unloading the residue. iv) be buried in the ground to help withstand pressure and act as an insulator. Often several digesters are used together to maintain a continuous supply of gas. It provides a useful way of getting rid of animal waste. (eutrophication) Osman Khan 12 RF 28/04/07 ...read more.

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