Fitri AnggraeniMutiara Adzhani Harinda

Widyasari Galuh Prabhandini

Crude oil, natural gas and coal are fossil fuels. Fossil fuels are very precious resources because they are non-renewable. We can also make lots of organic chemicals from them, needed to make products such as paints, detergents, polymers (including plastics), cosmetics and some medicines.

Fossil fuels were formed from the fossillized remains of dead plants and animals that once lived millions of years ago. Oil and natural gas are the products of the deep burial and decomposition of dead plants and animals. Heat and pressure, in the absence of oxygen, transform the decomposed material into tiny pockets of gas and crude oil. The oil and gas then migrates through the pores in the rocks to eventually collect in reservoirs.

Coal comes mainly from dead plants which have been buried and compacted beneath sediments. Most coal originated as peat in ancient swamps created many millions of years ago.

Crude oil is a complex mixture of hydrocarbons with small amounts of other chemicals such as sulphur. The crude oil is useless as a mixture and must be sent to an oil refinery to be separated. Crude oils from different parts of the world, or even from different depths in the same oilfield, contain different mixtures of hydrocarbons and other compounds. This is why they vary from light coloured volatile liquids to thick, dark oils.

A refinery is a factory. A refinery takes a raw material (crude oil) and transforms it into petrol and hundreds of other useful products. A typical large refinery costs billions of pounds to build and millions more to run and upgrade. It runs around the clock 365 days a year, employs  hundreds of people and occupies as much land as several hundred football pitches.

A REFINERY breaks crude oil down into its various components, which then are selectively changed into new products. This process takes place inside a maze of pipes and vessels. The refinery is operated from a highly automated control room.

All refineries perform three basic steps: Separation (fractional distillation) Conversion (cracking and rearranging the molecules) Treatment

1. Separation: fractional distillation Modern separation involves piping crude oil

through hot furnaces. The resulting liquids and vapours are passed into distillation towers

It is important to realise that the column is hot at the bottom and cool at the top.

The crude oil separates into fractions according to weight and boiling point.

The lightest fractions, including petrol and liquid petroleum gas (LPG), vapourise and rise to the top of the tower.

Kerosine (aviation fuel) and diesel oil, stay in the middle of the tower

Heavier liquids separate lower down. The heaviest fractions with the highest boiling

points settle at the very bottom.

Some fractions from the distillation towers need to be transformed into new components . This is where a refinery makes money, because the low-value fractions that aren't in great demand can be converted to petrol and other useful chemicals.

The most widely used conversion method is called cracking because it uses heat and pressure to "crack" heavy hydrocarbon molecules into lighter ones. A cracking unit consists of one or more tall, thick-walled, reactors and a network of furnaces, heat exchangers and other vessels. Catalytic cracking, or "cat cracking," is the basic petrol-making process. Using intense heat (about 600°C), low pressure and a powdered catalyst (a substance that speeds up a  chemical reaction), the cat cracker can convert most of the heavy fractions into smaller more useful molecules.

Some refineries also have cokers, which use heat and moderate pressure to turn the really heavy fractions into lighter products and a hard, coal like substance that is used as an industrial fuel.

Cracking and coking are not the only forms of conversion. Other refinery processes, instead of splitting molecules, rearrange them to add value. Alkylation makes petrol components by combining some of the gaseous byproducts of cracking. The process, which essentially is cracking in reverse, takes place in a series of large, horizontal vessels.

Treatment: the finishing touch Today, a major portion of refining involves

blending, purifying, fine-tuning and improving products to meet specific requirements. To make  petrol, refinery workers carefully blend together a variety of hydrocarbons. Technicians also add performance additives and dyes that distinguish the various grades of fuel. By the time the petrol is pumped into a car it contains more than 200 hydrocarbons and additives.

Example: Petrol companies produce different blends of fuels to suit the weather. In winter, they put in more volatile hydrocarbons (with short carbon chains) and in summer they add less volatile hydrocarbons to compensate for the higher temperatures.

LPG (Liquified Petroleum Gas)is a flammable mixture of hydrocarbon gases used as afuel in heating appliances and vehicles, and increasinglyreplacing chlorofluorocarbons as an aerosol propellant and arefrigerant to reduce damage to the ozone layer. Gasolineis a petroleum-derived liquid mixture which is primarily used as a fuel inInternal combustion engines. KeroseneKerosene is widely used to power jet-engined aircraft (jet fuel)and some rockets, but is also commonly used as a heating fueland for fire toys such as poi. Solar OilSolar oil used as diesel engine fuel. Usually, solar contains highcomposition sulfur in it. Grease Oil and AsphaltGrease oil used to prevent corrosion and minimize friction. Asphalt comes from earth

crudeoil reduce it used to layered road surface.