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MATHS@WORK
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Case 2 Optimising Production of Products from Crude Oil A refinery takes crude oil extracted from wells bored into the earth. Crude oil is a natural product formed over thousands of years by a transformation of plant life and organic materials which have been buried and exposed to high temperatures and pressures. At Fawley Refinery we take crude from all over the world including wells in the North Sea and Saudi Arabia. The composition of crude oil is not fixed or constant, it is not a scientific compound, but a mixture of many components that we separate in our processes and refine into useful products. Some examples of these many components are petrol, aviation fuel, liquefied petroleum gas and naphtha that are sold for various industrial and commercial uses. Each component has different properties and we separate them using distillation columns, which split the components according to their boiling point. Essentially, we heat up the crude oil and the light products, such as LPG, come off the top of the distillation column, streams such as petrol are taken out of the middle of the column and heavier products, such as the components used in motor oils or bitumen, come off the bottom of the tower. It is important for us to be able to calculate the proportion of these various components in our feed crude oil as each product is worth a different amount of money to the refinery and has an effect on the way we run our equipment. Chemical models of the various crudes are used to predict the overall refinery production and matched with the markets or demands for the various products. Below is a simple example of the type of calculation we use to determine what types of crude we use and in what amounts. Worked Example We have two crude oil feed streams that are blended to make up a single feed to a distillation column. For simplicity we will assume that the crude oil is being split into 3 components: Liquefied Petroleum Gas, Light Virgin Naphtha and Petrol. One crude comes from the North Sea oilrigs and one crude comes from Saudi Arabia. Each crude is composed of a different percentage of each product. We need to be able to calculate the percentage of LPG, LVN and petrol in each of the two feed crudes.
The table below shows the input flowrates of crude 1 and 2 and the resulting amounts of LPG, LVN and Petrol that come out of the distillation column.
This information can be shown diagrammatically CASE 1
CASE 2
All amounts are in m3/hr So in case 1, 100 m3/hr of crude 1 is mixed with 100m3/hr of crude 2 and 25, 45, 130 m3/hr respectively of LPG, LVN and Petrol are produced. Similarly for case 2. What are the percentages of each component in each crude? ANSWERS From the two cases above we can produce two simultaneous equations for each product.
So we have been able to determine the composition of the two feed streams of crude oil. In summary
Altering the flowrate of each crude will alter the mix of products. This in turn will have profit implications. We will consider these now.
Financial Implications
How much per day will we make in each case? Let us look at what we calculated the amounts of each of the three products to be in case 1
From these figures we can calculate the money made and the costs (In each case we multiply by 24 to calculate for a day rather than an hour) Money Made
Costs of Crude
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