The refining process
Crude oil is composed of several types of hydrocarbons. Oil refining is a process that takes advantage of the different weights, volatilities and boiling temperatures of hydrocarbons in order to separate them and create intermediary and finished products.
Usually, there are four major refining stages to separate crude oil into usable substances:
- physical separation of the several hydrocarbon types through distillation;
- purification of intermediary products in pre-treatment units;
- chemical processing of the less valuable fractions into lighter products;
- treatment and mixture of intermediary products by removing undesired elements for the integration in finished products.
The process starts with the heating of crude oil. The steam that is generated goes up a fractionating column equipped with compartments at different heights. The components with higher volatility and lower boiling points go to the top of the colum. The components with higher boiling points stay in the lower layers. This technique of physical separation of fractions is also called fractional distillation and is the starting point for the oil refining process.
Each step of the refining process is aimed at maximising the added value of processed materials. The most simple refineries only perform crude distillation. The most complex refineries also perform three other functions.
The refineries' configuration
The range and quality of the refined products that are produced in a refinery depends on the types of crude used as raw material and the structures installed in the refinery.
Light and sweet crude generate higher amounts of higher-value refined products, such as gasoline, jet fuel and diesel. The most heavy and sour crude produce higher amounts of lower-value products, such as fuel oils.
The configuration of some refineries, particularly in North America, is generally oriented towards the production of light distillate products, such as gasoline, while the configuration of refineries in the other world regions, like Europe, is generally oriented towards the production of middle distillate products, such as diesel and jet fuel. In addition, there are refineries configured to produce other specialised products, such as base oils, naphtha and bitumen.
The refineries are divided into two main categories: simple hydroskimming refineries and complex refineries. The simple hydroskimming refineries primarily execute the distillation process, while the complex refineries develop two additional functions: the conversion of the hydrocarbon fractions produced in the crude distillation process of other products and the treatment of middle products in order to obtain higher-value products. Therefore, simple refineries produce lower-value oil products than complex refineries for the same crude range.
The configuration of complex refineries is oriented towards the maximisation of both gasoline production (catalytic cracking) and middle distillate products (hydrocracking). In addition, these refineries use several secondary processing capacities to benefit vacuum residue.
Refineries configured to have a large conversion and desulfuration capacity can achieve higher returns in higher-value refined products, since they process heavier and sourer crude than refineries with lower conversion and desulfuration capacity.
A refinery's complexity is related to the capacity to process raw material, such as heavier crudes and with higher sulphur content, into value-added products. The higher is the complexity, more flexible is the crude range that the refinery can process and better positioned it is to take advantage of lower-cost crude, which leads to an increase in the refining margins.