Crude oil extracted from underground is not directly suitable for most uses. In a refinery, it is separated into fractions, converted to better meet demand and then treated to comply with market specifications. Fuels, domestic gas, bitumen and petrochemical feedstocks come from this industrial chain. In Africa, developing local capacity can reduce some imports, provided supply, markets and plant profitability are secured.
Key facts
- Objective: converting crude and other feedstocks into marketable products.
- Stages: distillation, conversion of fractions, then treatment and blending.
- Products: gasoline, diesel, kerosene, LPG, fuel oils, bitumen and petrochemical feedstocks.
- Distinction: a refinery's nameplate capacity does not necessarily correspond to its actual throughput or final output.
What is oil refining?
Refining encompasses processes that turn crude oil into products meeting specific uses and standards. Crude composition varies with origin: some oils are light and low in sulphur, while others are heavier or more sulphurous. A refinery adapts operations to these characteristics, its equipment and the needs of the markets it serves.
Crude is a complex mixture of hydrocarbons. Producing fuels or bitumen requires separating its fractions, modifying some of them and removing undesirable compounds.
First stage: separating fractions
Crude is first desalted and preheated, then heated to a high temperature. In an atmospheric distillation column, vapours rise and condense at different levels according to their boiling temperatures. The lightest components are recovered at the top; heavier fractions condense lower down. Products include gases, naphtha, kerosene, diesel and a heavy residue.
This initial fractionation is insufficient to produce all finished fuels. Some residue passes through a vacuum distillation unit. Reduced pressure allows other components to be separated without exposing them to temperatures that would cause degradation. The resulting fractions become feedstocks for conversion stages.
Distillation separates molecules according to their properties without changing their chemical structure. Conversion units allow yields to be adapted to fuel demand.
Second stage: converting fractions
Conversion processes modify molecular size or structure to produce more desired components. Catalytic cracking breaks heavy molecules into lighter ones, useful particularly for making gasoline and petrochemical feedstocks. Hydrocracking combines heat, pressure, a catalyst and hydrogen to convert heavy fractions into lighter products, including diesel and kerosene.
Other units complement these operations: reforming improves the octane rating of certain gasoline blending components, while coking processes heavy residues. The site's configuration determines its product range.
Third stage: treatment, blending and checks
Products from distillation and conversion still need contaminants removed or properties adjusted. Hydrodesulphurisation uses hydrogen and a catalyst to reduce sulphur content. Other treatments remove nitrogen compounds or improve product stability and performance. Environmental and technical specifications vary by market and use.
Treated components are then blended into finished products. Commercial gasoline may combine several blending components from different units and additives; aviation fuel, diesel and fuel oil must also meet quality criteria. Analyses check these characteristics before storage and shipment. The refinery must also manage by-products, energy consumption, industrial wastewater and emissions.
Which products come out of a refinery?
The range depends on crude and equipment. It includes gasoline, diesel, aviation fuel, LPG, petrochemical naphtha, fuel oils, lubricants and bitumen. Some units also recover sulphur from sulphurous crudes.
The proportions of gasoline, diesel or residue vary with equipment, crude and shutdowns. Total product volume may slightly exceed processed crude volume because conversion reduces average density.
Capacity, throughput and profitability: three distinct concepts
Nameplate capacity indicates the maximum volume of crude the facility is designed to process, generally per day. Actual throughput depends on supply, demand, shutdowns and economic choices; individual product volumes are a separate measure.
Profitability depends on product value relative to crude costs, as well as energy, logistics and maintenance expenditure. Complex facilities make better use of residues but require additional investment and skills. Size alone therefore guarantees neither profitability nor energy self-sufficiency.
In Nigeria, the Dangote refinery at Lekki illustrates the rise of large-scale assets on the continent. The operator states a crude distillation capacity of 700,000 barrels per day. This figure describes the distillation unit's announced capacity; it does not mean that the same volume is processed every day or that all products consumed in Nigeria are permanently covered. The effect on imports depends on operating levels, product grades, prices and domestic distribution.
Issues for Africa and the energy transition
Local refining can create industrial jobs, reduce some imports and supply petrochemical inputs. However, success depends on reliable supply, port and logistics infrastructure, sufficient markets and the ability to compete with imported products.
The sector must also invest in safety, effluent treatment and emissions reduction. In the longer term, energy efficiency, transport electrification and climate policies may change fuel demand. New projects must incorporate these developments into profitability assessments.
Frequently asked questions
Does refining remove every impurity from oil?
Processes reduce or eliminate certain compounds to meet product specifications. Treatment levels vary with crude, equipment and applicable standards; this is not a single purification process that makes every product identical.
Can a refinery produce only diesel?
No. It manufactures several products and intermediates in proportions linked to the crude processed and its units. Conversion processes can change these proportions, but every configuration retains technical and economic limits.
Why does an oil-producing country import fuels?
Producing crude does not mean having sufficient capacity to refine it. Imports may also address plant shutdowns, distribution problems, a mismatch between manufactured products and demand, or price considerations.