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87- www. energy- future. com 6.2- Understanding oil and gas Refining and petrochemicals: explained Crude oil straight out of the ground is pretty useless, but it becomes extremely useful after being refined into oil products such as gasoline, diesel and jet fuel. Indeed, it can be invaluable: if you ran out of fuel during a drive through the desert and were 200 kilometres from the nearest water source, would you rather have 50 litres of water or 50 litres of gasoline? Refineries come in many different sizes and configurations, depending on the size of the local market, the types of products needed and the types of feedstocks availa-ble for processing. But they all perform the same basic tasks: distilling crude oil into its various constituent fractions; chemically re-arranging low- value configurations of hydro-carbon molecules into high- value combina-tions to produce a variety of end- products, from gasoline to Tupperware; and treating those products to meet environmental and other specifications and standards by re-moving impurities such as sulphur. Carbon chains Crude oil can be split up into molecules of carbon and hydrogen in a variety of com-binations through the refining process. Depending on the length of the chains within them, they can be used in a variety of ways. For example, molecules used for cooking gas usually have up to four carbons, while gasoline for cars is a longer chain, of up to 12. Lubricants - motor oils, for example - are even longer, with perhaps 50 carbons. The different chain lengths in petroleum have different boiling points, so they can be separated by heating the crude and distilling the resulting vapour ( see p91). The first step is heating up the crude oil - once impurities such as water and salt have been removed from it. The heat is often gen-erated by burning fuel oil in a furnace. The vaporised petroleum, heated to about 350° C, is pumped into a fractionating tower - or atmospheric pipestill. As it rises up the tower, it cools down and its com-ponents condense back into several dis-tinct liquids, collecting in a series of trays. Lighter liquids, such as kerosene and naph-tha, a product used in chemicals process-ing, collect near the top of the tower, while heavier ones such as lubricants and waxes fall to the bottom. Vaporised petroleum, heated to about 350° C, is pumped into a fractionating tower

88- www. world- petroleum. org 6.2- Understanding oil and gas In addition to the various desired frac-tions, the process also produces a thick, heavy residue. This can be processed fur-ther in a vacuum- distillation unit, which uses a combination of high temperature and low pressure to make more useful products. At this stage of the refining process, jet fuel is pretty much ready for use in an air-craft, but most of the products aren't fin-ished: they're blendstocks or feedstocks for other processes. A combination of fur-ther heating, pressure treatment and the use of chemical catalysts is used to break the chemical bonds that link these chains to-gether and reconfigure them into new com-binations, yielding a host of desirable prod-ucts, such as gasoline. It's called cracking. A catalytic cracker can handle a number of feedstocks, including heavy gasoil, treated fuel oil and residue from the lubricant treat-ment plant. Mixing the feedstock with a hot catalyst enables the cracking reaction to take place at a relatively low temperature ( about 500° C). The products are then separated in a fractionating column. Another refining process, reform-ing, uses heat and pressure in the pres-ence of catalysts to convert naphtha feed-stock into higher- octane, gasoline- blending components. The finished products - with marketable octane ratings and specific engine properties - are then stored in tanks on the refinery's premises, before being loaded onto barges, ships and trucks, or into special pipelines for transportation to market. Not surprisingly, big petrochemicals complexes are often found close to big oil deposits, or on the coast, so crude can be easily imported and products easily shipped out. Cracking move To get more value out of their processed crude, energy companies shift into the realm of the petrochemicals plant, which uses pe-troleum- based feedstock - naphtha, for in-stance - to create new products, such as the plastics to be found in a welter of eve-ryday products, from computers and mobile phones to cars and toys. This is achieved by converting the feed-stock into substances such as olefins ( a group that includes ethylene and propyl-ene) and aromatics ( the distinctive smell-ing chemicals like benzene and toluene). These in turn provide the foundations for a range of familiar materials, including pol-yester, vinyl acetate, polystyrene, poly-urethane, detergent alcohols, synthetic rubber and many more products. Finished products are stored in tanks on the refinery's premises before being transported to market © Statoil/ Bergs oljehamn