Feature Report: About Refining

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Why Crude Oil Needs to be Refined

Crude oil needs to be refined in order to transform it into a range of useful products for industry and consumers.

Refining converts crude oil into products that can be used by consumers and industry. © THINKSTOCK

Refining Crude Oil for Use

The gasoline or dieselDiesel is the name of an internal combustion engine that works by compression-ignition... we put in our car, the fuelFuel is any solid, liquid or gaseous substance or material that can be combined with an oxidant... oil we burn to heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... our homes in winter and the natural gas we use to cook are all fuels and sources of heat derived from oil and gas extracted from deposits across the globe.

Roughly speaking, crude oilOil that has not been refined. is a “mixture” of all these energy products. To meet user requirements, it must be separated, converted and treated in a process known as refining.

Could crude oil be used directly if only we had the right kinds of engines and boilers? The answer is no, because each crude oil is very different and made up of a large number of hydrocarbonOrganic compound consisting of carbon and hydrogen. Hydrocarbons are the principal constituents of crude oil, natural gas and petroleum products. molecules. The lightest molecules, dissolved gases, have 1 to 4 carbon atoms, while the heaviest have over 20. These molecules are present in varying proportions depending on the depositAn accumulation of natural resources, such as oil, natural gas, coal, uranium, metal ore or another commodity..., meaning that each oil has its own composition and properties. Some crudes are black and viscous and contain a lot of heavy molecules; others are brown, more fluid and lighter. Each also contains a certain amount of dissolved gas and highly corrosive products, such as sulfur or acids, which can sometimes be toxic.

Crude oil is a highly variable mixture of heavy and light hydrocarbons that need to be separated in a refinery to turn them into usable products. 

For these different reasons it is impossible to develop a universal boiler or engine capable of running on all crude oils.

Solutions That Meet Consumer Demand

Demand for petroleum products has changed significantly since the mid-20th century. In industrialized countries, the development of road and air transportation has accelerated, leading to stronger demand for light products, such as fuel. At the same time, the consumption of heavy fuel oilHeavy fuel oil is high-viscosity liquid fuel, used in big diesel ship engines or as a thermal power plant fuel.... has declined as other energy sources, such as gas and nuclear powerIn physics, power is the amount of energy supplied by a system per unit time. In simpler terms, power can be viewed as energy output..., are being used for heating and power generation.

Today, global demand for petroleum products breaks down roughly as follows:

The only crude oil that more or less matches these percentages before refining is Algeria’s light Saharan Blend. All other crudes contain a larger percentage of heavy products. The average breakdown of distillates obtained by separation of crude oil is significantly different from the breakdown in demand:

  • 25% for light distillates.
  • 35% for middle distillates.
  • 40% for heavy distillates. To align production with demand, it is therefore necessary to convert some of the heavy products into light products before bringing them to market. These lighter products are more expensive than crude oil, because their price includes refining costs.

To obtain products that satisfy current consumer and industry demand, specially designed production and conversion units featuring innovative refining processes have been built. (See Close-Up: "The Three Stages of Refining")