An oil refinery could also be thought of as a factory that converts crude oil into a range of useable merchandise. It is designed to supply what the market requires in probably the most economical and efficient method. Step one in the manufacture of petroleum products is the separation of crude oil into the primary fractions by atmospheric distillation. When crude oil is heated, the lightest and most volatile hydrocarbons boil off as vapours first and the heaviest and least unstable last. The vapours are then cooled and condensed back into liquids.
This distillation process is carried out in a fractionating column. That is divided into a series of chambers by perforated trays, which condense the vapours at each stage and allow the liquids to circulation into storage tanks. Pre-heating of the crude oil is restricted to 350°C to stop the oil being thermally cracked.
Atmospheric and Vacuum Distillation
The residue from atmospheric distillation is typically known as lengthy residue and to recuperate extra distillate product, additional distillation is carried out at a decreased pressure and high temperature. This vacuum distillation course of is important in maximising the upgrading of crude oil. The residue from vacuum distillation, typically referred to as short residue, is used as a feedstock for additional upgrading or as a gas part. Unlike the fractionating column for atmospheric distillation, a system of packed beds as an alternative of trays is used for condensation of the low-pressure vapours.
Refineries based mostly simply on atmospheric and vacuum distillation are stated to be working “the straight run course of and the fuel oil is principally either long or brief run residue. The percentage of residue varies depending on the composition of crude processed. For a typical “light North African crude the residue is 28%, while for a “heavy Venezuelan crude it is as high as eighty five%. The proportion of products produced doesn’t at all times match the product demand and is primarily decided by the crude oil.
In order to satisfy the product demand, additional refining processes had been launched. At the moment, a modern refinery, in addition to atmospheric and vacuum distillation, may additionally encompass secondary refining processes reminiscent of cracking, which may be thermal or with a catalyst. A typical trendy refinery installation is proven below. Thermal cracking is the oldest and in principle the only refinery conversion process. It is carried out over a wide range of temperatures, between 450-750°C and pressures from atmospheric to 70 bar. The temperature and strain depends upon the type of feedstock and the product requirement. At these elevated temperatures, the large hydrocarbon molecules turn into unstable and spontaneously break into smaller molecules.
Another vital factor in the process is the residence time. The feedstock will be either the residue from the atmospheric or vacuum distillation units, or a mixture of the two. In modern refineries, there are three major functions of the thermal cracking process: visbreaking, a thermal gas oil unit and coking. Visbreaking is the most vital process with regard to the manufacture of residual gasoline oil. It is a mild type of thermal cracking usually used for lowering the viscosity of straight-run residual fuels. Normally such fuels are very viscous and, if required for sale as heavy gasoline oil, should be blended with a comparatively high worth distillate to meet the completed product specification.
Visbreaking reduces the quantity of distillate required as diluent or “cutter stock This materials can then be profitably diverted elsewhere. The primary purpose of a thermal gasoline oil unit is to supply and get well the utmost quantity of gasoline oil. In extreme circumstances, the viscosity of the residue could also be larger than that of the feed stock. Coking is a extreme form of thermal cracking. It is designed to convert straight-run residues into extra useful products resembling naphtha and diesel oil. As well as, gas and coke are produced and thus this course of doesn’t feature within the manufacture of residual fuel oils.
Catalytic cracking is the most important course of in the petroleum refining industry for the conversion of heavy hydrocarbon fractions, mainly into excessive-high quality gasoline and gas oil components. These are lighter, less viscous and more priceless than the feedstock. There are numerous different catalytic cracker designs however in all cases the product output can finally be separated to: gases, gasoline blending elements, catalytically cracked cycle oils and cycle oil slurry. The cycle oils are crucial with respect to residual fuel oil since they’re used as cutter stocks to cut back the viscosity of residues. Prior to make use of as a cutter stock, the cycle oil slurry must be treated to take away entrained cat fines. In a fashionable refinery, there’s a wide range of residues and diluent available for the production of gasoline oil. Usually the gas will encompass visbroken residue diluted with cycle oils and smaller quantities of different distillates.
The determine beneath shows the main streams of feedstock, fuel oil diluent and gas oil residues in a modern refinery. Clearly, if a refinery does not have a thermal cracking facility (visbreaker or thermal gasoline oil unit) then the gas oil will likely be based on lengthy or brief residue. Additional to the principle residual fuel streams in a modern refinery, it needs to be appreciated that different developments have taken place to further maximise the manufacturing of gasoline, kerosene and diesel from a barrel of oil.
One of those is by residue hydroconversion the place residual fractions are converted into feedstock, which in turn may be further processed in typical crackers to yield lighter products. Maximisation of manufacturing for the lighter merchandise is carried out on the expense of residual gasoline oil.