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The petrol or diesel that we put in the tank of our car, the domestic heating oil that we burn for heating in the winter, the cylinder of gas which contributes to the delicious
dishes we prepare, and all the chemical products that play a part in our everyday lives… they all come from oil. But we never use crude oil directly.
Why is that? Why aren’t there motors and boilers that run on crude oil? The reason is very simple: crude oil is an unstable mixture of several hydrocarbons, in varying quantities according to the density of the product, and there is not just one crude oil, but a multitude of different crudes. In fact, each oil field has its own history and its own particular composition of different hydrocarbons. Some, black and viscous, contain many heavy molecules. Others, brown and freer flowing, are lighter. They contain more or less dissolved gas. And all of them contain varying proportions of sulphuric or acid products, very corrosive for metals. Of course, a universal motor adapted to each and every fuel doesn’t exist, nor does a boiler that is resistant to very aggressive corrosive action.
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| The refinery at Anvers (Belgium). |
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That is why the crude oils must be purified and transformed into products having an almost constant composition, well adapted to their use. These transformations are carried out in refineries. |
| But the overriding objective of a refiner is to respond to the demand for petroleum products. Today, the development of road and air transport has accelerated, and the demand for light products has soared. At the same time, we burn a lot fewer heavy products to produce electricity or for heating. Worldwide demand is for about 40% light products (automotive fuels), 40% middle range products (boiler fuel, diesel) and 20% heavy products. The only crude oil corresponding more or less to these proportions is the light crude from the Algerian Sahara. But the majority of crudes extracted in the world contain more heavy products. Refineries composed uniquely of a single distillation tower, as in the past, are therefore no longer sufficient. |
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| Extra-heavy oil. |
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Other production plant is necessary in order to transform (we also say to convert) the heavy products into light products. Several refining techniques exist to do this. It is because of the costs of transformation that the heavy crude oils are less expensive than the light oils. |
| This need to adapt refineries to the demand for petroleum products also explains the location of refineries throughout the world [link to focus: Where are the refineries situated?. A lot of them are in the developed countries, the very large consumers, even in those that do not have any oil! By constructing refineries on their own territory, they guarantee for themselves an independent refining policy. |
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| The crude oil refinery at Feyzin (France). |
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