Comparing Fuel Sources

COMPARING FUEL SOURCES Defining fuels Fuels are materials that contain stored chemical energy that can be released easily. When released, this energy is in the form of heat or power. Example Sucrose, a type of sugar, can be used to power your body. Countries use energy for transportation and heating. The energy in fuels is denoted by the SI (international standard for units) unit Joules (J). Because materials often store significant amounts of energy, energy is often provided in a range of units: ● kilojoules, 1 kJ = 10^3 J ○ 6 megajoules, 1 MJ = 10 J ● gigajoules, 1 GJ = 10^9 J ● terajoules, 1 TJ = 10^12 J There are a range of materials that are considered fuels: 1. petrol 2. diesel 3. LPG (liquid petroleum gas) 4. wood 5. natural gas 6. ethanol etc. These are classified by their source; as either fossil fuels or renewable energies. This depends on whether the fuel source is sustainable and/or renewable. Sustainable means the fuel is able to support energy and resources into the future without depletion. Renewable means the fuel able to be constantly replenished or are not finite (e.g. wind). This means that non-renewable resources can be sustainable if used in moderation, such as timber. Fossil fuels are defined as non-renewable. This means that they are used much faster than they can be replaced. It includes coal, oil, and natural gas. These sources all have a finite amount and will run out. They often take millions of years to form and so are being used much faster than they can be replenished. Because they will run out, fossil fuels are becoming more and more expensive and they also greatly contribute to greenhouse gases formation, and by extension, climate change. The negative impacts and cost of fossil fuels have caused a big shift towards using new sources of fuels that are renewable (beyond using solar, wind, hydro and tidal). These biochemical fuels or biofuels are ideally obtained from natural sources can quickly replenished and therefore will not run out easily. They are typically derived from plant materials including maize (corn), wheat, barley, sugar cane and vegetable waste or vegetable oil. These plant materials grow using photosynthesis, which removes carbon dioxide from the air. This helps to balance the carbon dioxide produced when burnt. The three main biofuels are: 1. biogas, 2. bioethanol 3. biodiesel. Case Study In 2019, Australia produced 79% of its power using fossil fuels (including coal 52%, gas 21%, oil 2%) and 21% from renewable sources (including solar 7%, wind 7%, hydro 5%). The share of renewable energy increased from 19% in 2018 and will continue to increase as renewable become cheaper than fossil fuels and countries act against climate change. Coal as a fuel Coal is formed from broken down wood and other plant/animal materials in a process that takes millions of years. These materials are mostly made of carbon. As more wood is converted into coal, the percentage of carbon increases. The percentage of hydrogen and oxygen also decreases, meaning the coal progressively becomes dryer through loss of water and so burns better (releases more heat energy). The decomposing wood becomes peat, brown coal and then black coal. Coal is primarily composed of carbon, hydrogen, nitrogen and sulfur. Crude oil as a fuel Crude oil (or petroleum) is a fossil fuel that is composed of a mixture of hydrocarbon molecules - mostly alkanes of the homologous series. Crude oil is not useful as a fuel, but can be separated into many different components that have a variety of uses. Crude oil is separated by fractional distillation. This process uses heat to separate compounds as gases in a tower. As the heat decreases up the length of the tower, the different temperatures separate the hydrocarbon mixtures based on boiling point. Along the inside of the tower are many trays containing liquid that the gas is bubbled through. If a gaseous component has a similar boiling point to this liquid, then it is collected in the tray and does not go further up the tower. Consequently, fractions collected from trays higher in the tower will have lower boiling points. Each fraction obtained from fractional distillation is not pure, but contains a fraction of similar hydrocarbons. This process can separate out longer hydrocarbons (used for bitumen, lubricating oils etc. with > 20 carbons) from diesel (12-20 carbons) to petrol (8- 12 carbons) to LPG (1-4 carbons). Natural gas & LPG as a fuel Natural gas is a fossil fuel found in the Earth's crust that is primarily composed of methane (CH4), with small amounts of other hydrocarbons like ethane and propane. Water, sulfur, carbon dioxide and nitrogen are also found in natural gas. Natural gas is found in gas reservoirs trapped between layers of rock, a component of petroleum (crude oil) deposits, attached to the surface of coal deposits (coal seam gas), or trapped in shale rock (shale gas). Natural gas is obtained from coal or shale deposits through a process called fracking. Fracking is used to release the natural gas attached to the surface of coal (coal seam gas) or shale rock. Deep wells are drilled into the Earth's crust and lined with steel and concrete. Then, fracking fluid is pumped down the well into the shale rock or coal, causing it to crack which releases the gas. The gas then flows back up the well and is collected. Fracking fluid includes sand, water and many other chemicals (e.g. benzene, toluene, xylene and ethylbenzene). It is of significant concern to the environment and underground water supplies if the toxic fracking fluid leaks out. LPG (liquified petroleum gas) is isolated from natural gas and is used as fuel in cars and in home gas bottles. Propane and butane gas can be separated from natural gas using fractional distillation. Both propane and butane become liquids under pressure and is sold as LPG. The remaining natural gas is used for home heating and cooking. Bioethanol as a fuel Bioethanol is ethanol produced from starches and other sugars catalysed by enzymes from yeasts. These enzymes catalyse the breakdown of starches in grain crops to glucose. The glucose is then further converted to ethanol by fermentation, which also releases carbon dioxide. The chemical formula the fermentation of glucose is C6H12O6(aq) → 2C2H5OH(aq) + 2CO2(g) Bioethanol is used extensively throughout Australia, including in E10 petrol. E10 petrol contains up to 10% ethanol which is still compatible with car petrol engines. This reduces the consumption of crude oil derived petrol. Biogas as a fuel Biogas is gas produced from organic waste by anaerobic bacteria. These bacteria decompose the organic waste (carbohydrates and proteins) down into simpler carbon dioxide and methane. This occurs deep within the organic waste piles where oxygen concentration is extremely low. Biogas is primarily composed of methane (~60%) and carbon dioxide (32%). Farm manure, rotting vegetable waste and other waste is combined with anaerobic bacteria in an air-free tank or deep under a large pile of rubbish leading to the production of biogas. Biodiesel as a fuel Biodiesel is a mixture of organic compounds containing ester functional groups. These esters are produced by a chemical reaction between vegetable oil or animal fat (triglycerides) and an alcohol (most commonly methanol). The products are typically methyl esters.