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ENERGY CONVERSION MME 9617A Eric Savory www.eng.uwo.ca/people/esavory/mme9617a.htm Lecture 4 – Fuels Department of Mechanical and Material Engineering University of Western Ontario Aim: To examine the different fuel sources These include: Fossil fuels - Coal - Fuel oil - Natural gas - Bitumen Synthetic fuel Fossil fuels • Four main types: Coal, fuel oil, natural gas and bitumen • Fossil Fuels are hydrocarbons, formed from the remains of dead plants and animals. Fossil fuel is a general term for buried combustible geological deposits of organic materials, formed from decayed plants and animals that have been converted to crude oil, coal, natural gas or heavy oils by exposure to heat and pressure in the earth's crust over hundreds of millions of years. • The chemical compound is Cx(H20)y, which is produced by plants through photosynthesis where solar energy is converted to chemical energy. • Most of the fossil fuels were ‘produced’ in the Carboniferous Period of the Paleozoic Era: 299 - 359 million years ago. • The fuel formulation is: CnH2n+2. Fossil fuels • Coal - it is composed primarily of carbon along with assorted other elements, including sulphur. • Fuel oil - it is made of long hydrocarbon chains, particularly alkanes, cycloalkanes and aromatics. • Natural gas - consisting primarily of methane (CH4) but including significant quantities of ethane (C2H6), propane (C3H8), butane (C4H10), carbon dioxide, nitrogen, helium and hydrogen sulphide. It is found in oil fields, natural gas fields and in coal beds. Fossil fuels Bitumen – it is a mixture of organic liquids that are highly viscous, black, sticky, entirely soluble in carbon disulphide (CS2), and composed primarily of highly condensed polycyclic aromatic hydrocarbons (PAHs). Bitumen is primarily used for paving roads. Its other uses are for general waterproofing products, including the its use in the production of roofing felt. Oil shale - is a general term applied to a group of rocks rich enough in organic material (called kerogen) to yield petroleum upon distillation. Coal • Coal is formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geological time. • Coal was formed in swamp ecosystems which persisted in lowland sedimentary basins. These swamp environments were formed during slow subsidence of passive continental margins, and most seem to have formed adjacent to estuarine and marine sediments. • When plants die in these peat swamp environments, their biomass is deposited in anaerobic aquatic environments where low oxygen levels prevent their complete decay by bacteria and oxidation. Burial by sedimentary loading on top of the peat swamp converts organic matter to coal by: - Compaction, due to loading of the sediments on the coal which flattens the organic matter - Removal of water held within the peat in between the plant fragments - Ongoing compaction removal of water from the intercellular structure of fossilized plants - Heat and compaction removal of water - Methanogenesis; similar to treating wood in a pressure cooker, methane is produced, which removes hydrogen and some carbon, and some further oxygen (as water) - Dehydrogenation, which removes hydroxyl groups (OH) from the cellulose and other plant molecules, resulting in the production of hydrogen-reduced coals Generally, to form a coal seam 1m thick, some 10 - 30m of peat is required. Peat has a moisture content of up to 90%. Coal formation Coal mining • The most economical method of coal extraction from coal seams depends on the depth and quality of the seams, and also the geology and environmental factors of the area being mined. • Surface and mountain top mining – If the coal seams are near the surface, the coal is extracted by strip mining. Strip mining exposes the coal by the advancement of an open pit or strip. – Mountain top removal is a form of surface mining that takes place at the topmost portion of a mountain. Utilized for the past 30 years, mountain top mining involves removing the highest part of the mountain for the maximum recovery of coal. • Underground mining – Most coal seams are too deep underground for open cast mining and thus this type of mining is called underground mining. In deep mining, the room and pillar method progresses along the Mammoth coal vein seam, while pillars and timber are left standing to support the coal mine roof. Petroleum (oil, gas) Petroleum forms from the remains of plants and animals that lived in the ocean 10-160 million years ago. When organisms died and sank to the bottom, they were covered in mud, sand, and other mineral deposits. This rapid burial prevented immediate decay, which would normally occur if the organisms remained exposed on the sea floor. The lack of oxygen in the sedimentary layers caused organisms to slowly decay into carbon-rich compounds. These compounds mixed with surrounding sediments and formed source rock, which is a type of fine-grained shale. As more layers were deposited on top of one another, pressure and heat acting on the source rock compressed the organic material into crude oil. Petroleum – finding oil • Discovering the location of oil within the earth is difficult because of the presence of cap rock, which can be miles thick in some locations. Oil geologists study surface rocks and the terrain to determine if any oil is present underground, but the best evidence comes from various satellite imaging techniques. • Oil flows may disrupt the earth's gravitational or magnetic field and so gravity meters and magnetometers can detect some oil sources. • The most reliable method for finding oil is through the use of shock waves in a process called seismology. In a seismological survey a shock wave is aimed at the surface of the water or land and the length of time it takes for the waves to reflect back to the sensor is recorded. The speed of the shock wave depends on the type of rock it travels through, and by comparing the travel times to known densities of rock, seismologists can determine what rocks are underground and predict if they might contain oil. Petroleum – production • The most common method of obtaining petroleum is extracting it from oil wells found in oil fields. • Primary recovery methods are used to extract oil that is brought to the surface by underground pressure and can generally recover about 20% of the oil present. • After the oil pressure has depleted to the point that the oil is no longer brought to the surface, secondary recovery methods draw another 5 to 10% of the oil in the well to the surface. • Finally, when secondary oil recovery methods are no longer viable, tertiary recovery methods reduce the viscosity of the oil in order to bring more to the surface. Crude oil refinement – fractional distillation Oil shale – fine grained sedimentary rock containing kerogen • The kerogen in oil shale can be converted to oil by the chemical process of pyrolysis, during which the oil shale is heated to 445 - 500°C in the absence of air (=pyrolysis) and the kerogen is converted to oil and separated out, a process called "retorting". • Oil shale has been burnt directly as a low-grade fuel. • It was estimated that in earth’s crust there are 6.5x1015 Tons of oil shale, about 1,000 times more than coal. • The US Energy Information Administration estimates the world supply of oil shale at 2.6 trillion barrels of recoverable oil, 1.0-1.2 trillion barrels of which are in the US. However, attempts to develop these reserves have been going on for over 100 years with limited success. • The caloric value of oil shale is 100 times smaller than coal. Crude oil production from oil shale Synthetic Fuels Introduction • Synthetic fuel or synfuel is any liquid fuel obtained from coal, natural gas, or biomass. It can sometimes refer to fuels derived from other solids such as oil shale, tar sand, waste plastics, or from the fermentation of biomatter. It can also refer to gaseous fuels produced in a similar way. • The process of producing synfuels is often referred to as Coal-To-Liquids (CTL), Gas-ToLiquids (GTL) or Biomass-To-Liquids (BTL), depending on the initial feedstock. Motivation • Synthetic fuels require a relatively high price of crude oil in order to be competitive with petroleum-based fuels without subsidies. However, they offer the potential to supplement or replace petroleum-based fuels if oil prices continue to rise. Several factors make synthetic fuels attractive relative to competing technologies such as biofuels, ethanol / methanol or hydrogen: – The raw material (coal) is available in quantities sufficient to meet current demand for centuries – It can produce gasoline, diesel or kerosene directly without the need for additional steps such as reforming or cracking – There is no need to convert vehicle engines to use a different fuel – There is no need to build a new distribution network Substitute Natural Gas (SNG) • Infrastructure of gas supply near coal mining. • The obtained gas is often Methane; CH4 which has a caloric value of ~ 1,000 Btu/scf. • Gasification is a process that converts carbonaceous materials, such as coal, petroleum, or biomass, into carbon monoxide and hydrogen. • Produces High Btu Gas (1,000) & Low Btu Gas (500). • The gas tends to be cheaper than coal. • The gas production technology is ‘simple’.