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Fractional Distillaton, Lecture 01, Fuel Tech-ll.pptx

  1. The various components of crude oil have different sizes, weights and boiling temperatures; so, the first step is to separate these components. Because they have different boiling temperatures, they can be separated easily by a process called fractional distillation. The steps for fractional distillation are discussed below.
  2.  Heat the mixture of two or more substances (liquids) with different boiling points to a high temperature. Heating is usually done with high pressure steam to temperatures of about 1112 degrees Fahrenheit / 600 degrees Celsius. The mixture boils, forming vapor (gases); most substances go into the vapor phase.  The vapor enters the bottom of a long column (fractional distillation column) that is filled with trays or plates. The trays have many holes or bubble caps (like a loosened cap on a soda bottle) in them to allow the vapor to pass through. They increase the contact time between the vapor and the liquids in the column and help to collect liquids that form at various heights in the column. There is a temperature difference across the column (hot at the bottom, cool at the top).
  3.  The Vapor Rises As the vapor rises through the trays in the column, it cools. When a substance in the vapor reaches a height where the temperature of the column is equal to that substance's boiling point, it will condense to form a liquid. (The substance with the lowest boiling point will condense at the highest point in the column; substances with higher boiling points will condense lower in the column.). The trays collect the various liquid fractions. The collected liquid fractions may pass to condensers, which cool them further, and then go to storage tanks, or they may go to other areas for further chemical processing.
  4. The oil refining process starts with a fractional distillation column. On the right, you can see several chemical processors that are described in the next section. Very few of the components come out of the fractional distillation column ready for market. Many of them must be chemically processed to make other fractions. For example, only 40% of distilled crude oil is gasoline; however, gasoline is one of the major products made by oil companies. Rather than continually distilling large quantities of crude oil, oil companies chemically process some other fractions from the distillation column to make gasoline.
  5. The top distillates The top of the fractionating column gives rise to gases and liquids that have short carbon chains in their composition. While these products are often used as fuels, many have industrial and chemical uses too.  Petroleum gases : Butane and propane and other petroleum gases are formed right at the top of the distillation tower, where it is coolest, a very mild 25°C: the temperature range that forms these gases is between 25°C and 50°C. These gases are the lightest products formed in crude oil distillation and are flammable gases.  Petrol These gases, being the lightest products formed and flammable gases too, are then processed into Liquified Petroleum Gas (LPG), which is usually a mixture of propane and butane. LPG is used for heating applications and also hot air balloons in the case of propane.  Naphtha The petroleum gases have four or five hydrocarbons in their chain. For these distillates, hydrocarbon chains are made up of three carbon atoms in the case of propane (C3H8), and four carbon atoms in the case of butane (C4H10).
  6. The middle distillate fuel oils Oils below this point have a flashpoint of higher than 42°C and are classified as fuel oils. These are the middle distillates as they form in the mid-section of the tower.  Paraffin: Used for heating and burning in domestic applications is paraffin and paraffin wax, which forms in the column at a range of 100°C to 175°C. Paraffin has between twenty and forty carbon atoms. Paraffin wax is further processed to be used in industry to create candles, petroleum jelly that protects skin and many other products.  Kerosene: While paraffin can also refer to kerosene, it comes as a result of paraffin’s history as a domestic heating fuel, which kerosene is now the default.  Diesel: Paraffin comes in both liquid and solid form and is used throughout the UK in a wide range of industries. It’s an extremely versatile product, and so has a wide range of uses including heating oil, beauty products, candles and medicines.
  7. Lower distillates At the bottom extremity of the fractioning tower, the lower distillates form. These have high densities, higher boiling points and are not used as fuels, but more as grease for lubrication. These form at temperatures of 350°C to 600°C.  Lubricating oil  Bunker fuels and heavy fuel oil  Marine gas oil (MGO)  Heavy fuel oil (HFO)  Marine fuel blends  Marine diesel oil (MDO)  Intermediate fuel oil (IFO)  Marine fuel oil (MFO) In between MGO and HFO are three additional maritime oils, MDO, IFO and MFO. These are produced by blending MGO with HFO in varied proportions.
  8.  Bituminous coal Bituminous coal is a soft, dense, black coal. Bituminous coal often has bands of bright and dull material in it. Bituminous coal is the most common coal and has a moisture content less than 20 %. Bituminous coal is used for generating electricity, making coke, and space heating. Bituminous coal has calorific values ranging from 6.8 - 9 kW/kG approximately  Anthracite coal Often referred to as hard coal, anthracite is hard, black and lustrous. Anthracite is low in sulphur and high in carbon. It is the highest rank of coal. Moisture content generally is less than 15 %. Anthracite has calorific values of around 9 kW/kG or above
  9. Residuals When it comes to petroleum products that are produced to ultimately be burned, it’s essential that waste is absolutely minimised, so at the bottom of the distillation tower, where temperatures reach 500°C to 600°C, the residue of crude oil is retrieved and put to use. Residue formed at the bottom of the fractionating column includes bitumen and asphalt.  Bitumen: Refined bitumen is made from the residue of petroleum refining, where the column is around 600°C. You’ll have come across it every day as it is an essential component of construction – used in tarring roads, sealing roofs and many other applications.  Asphalt: Bitumen also forms naturally – known as crude bitumen.
  10. END