Oil refinery: Processes, history and operations

Overview

An oil refinery, also known as a petroleum refinery, is an industrial process plant designed to transform crude petroleum into a variety of usable products. These facilities are critical nodes in the global energy infrastructure, converting raw feedstock into essential commodities such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefied petroleum gas, and petroleum naphtha. In addition to these standard refined products, modern refineries can also produce petrochemical feedstocks like ethylene and propylene. This production can occur directly through the cracking of crude oil, bypassing the need to first refine the crude into intermediate products such as naphtha.

The crude oil feedstock processed in these plants typically originates from upstream oil production plants. To manage the flow of materials, there is usually an oil depot located at or near the refinery. This infrastructure is used for the storage of incoming crude oil feedstock as well as bulk liquid products before they are distributed to end-users or further processing stages. The operational status of these facilities is generally classified as operational, serving as continuous conversion hubs in the energy supply chain.

Global refining capacity reflects the scale of this industrial sector. In 2020, the total capacity of global refineries for crude oil was about 101.2 million barrels per day. This figure represents the aggregate throughput potential of refineries worldwide, indicating the volume of crude oil the global network can process within a single day. The capacity is measured in barrels per day, a standard unit for quantifying petroleum production and processing rates.

The structure of a typical refinery involves multiple unit operations that separate and convert the hydrocarbons found in crude oil. While the specific configuration can vary depending on the crude quality and desired product mix, the core function remains the transformation of mixed hydrocarbon chains into distinct fuel types and chemical precursors. The presence of storage depots ensures that the refinery can maintain a steady supply of feedstock and buffer the output of bulk liquid products, smoothing out variations in production and consumption rates.

History of petroleum refining

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How do oil refineries work?

Oil refineries function as complex industrial process plants designed to transform raw petroleum into a diverse array of usable products. The refining process begins when crude oil, typically processed by an oil production plant, arrives at the facility. There is usually an oil depot at or near the refinery for the storage of this incoming crude oil feedstock as well as the resulting bulk liquid products. Before entering the main distillation columns, the crude oil often undergoes desalting to remove water and dissolved salts, which helps prevent corrosion and fouling in downstream equipment.

Distillation Processes

The core of the refining operation is distillation, which separates crude oil into different fractions based on their boiling points. Atmospheric distillation is the first major step, where crude oil is heated and passed through a tower under atmospheric pressure. This process separates lighter components such as gasoline, kerosene, and diesel fuel from heavier residues. For the heavier fractions that remain after atmospheric distillation, vacuum distillation is employed. By reducing the pressure in the distillation column, heavier oils can be separated at lower temperatures, preventing thermal degradation and yielding products like lubricating oils and residual fuel oils.

Cracking and Conversion

To maximize the yield of high-demand products, refineries use cracking processes to break down larger, heavier hydrocarbon molecules into smaller, lighter ones. This is crucial for producing gasoline and diesel from heavier crude fractions. In addition to traditional cracking of refined products, petrochemical feedstock like ethylene and propylene can also be produced directly by cracking crude oil. This direct crude cracking method operates without the need of using refined products of crude oil such as naphtha, offering an alternative pathway for petrochemical production. Other processes further convert and treat these fractions to produce final products including asphalt base, heating oil, liquefied petroleum gas, and petroleum naphtha.

The scale of these operations is significant. Each refinery integrates these various unit operations—distillation, cracking, and conversion—to optimize the output mix based on market needs and the specific characteristics of the crude oil feedstock.

What are the main products of an oil refinery?

Oil refineries serve as critical industrial process plants where raw petroleum is transformed into a diverse array of refined products essential for global energy and material needs. The primary outputs of this refining process include transportation fuels such as gasoline, also known as petrol, and diesel fuel, which power a significant portion of the world’s vehicles and machinery. In addition to these liquid fuels, refineries produce fuel oils and heating oil, which are widely used for residential heating and industrial power generation. Kerosene is another key product, utilized for aviation fuel and domestic lighting and heating. The refining process also yields asphalt base, a fundamental component in road construction and infrastructure development.

Petrochemical Feedstocks and Byproducts

Beyond traditional fuels, oil refineries are vital sources of petrochemical feedstocks. These include petroleum naphtha, which serves as a primary raw material for the production of plastics and synthetic fibers. Additionally, refineries can produce ethylene and propylene directly through the cracking of crude oil. This direct cracking process allows for the creation of these essential chemical building blocks without the intermediate step of using refined naphtha, offering flexibility in petrochemical production strategies.

The refining process also generates several significant byproducts. Sulfur is commonly extracted from crude oil during desulfurization, resulting in a valuable commodity used in fertilizer production and chemical manufacturing. Petroleum coke, or petcoke, is another major byproduct, formed during the thermal cracking of heavy residual oils. This carbon-rich material is used as a fuel source in power plants and as an anode material in the aluminum industry. The diversity of these outputs highlights the refinery's role not just as a fuel producer, but as a complex chemical processing hub that maximizes the utility of every barrel of crude oil.

Chemical processes in refining

Refining crude oil into marketable products requires a series of complex chemical and physical processes. These processes transform the hydrocarbon mix found in crude oil into specific fractions with desired properties. The primary units involved include hydrodesulfurization, catalytic reforming, fluid catalytic cracking (FCC), hydrocracking, alkylation, and coking. Each unit addresses specific characteristics of the feedstock to optimize yield and quality.

Hydrodesulfurization and Catalytic Reforming

Hydrodesulfurization (HDS) is a critical process for removing sulfur from natural gas and refined petroleum products. This unit reacts the feedstock with hydrogen in the presence of a catalyst to convert organic sulfur compounds into hydrogen sulfide. The resulting hydrogen sulfide is then removed, reducing the sulfur content of the final product. This process is essential for meeting environmental regulations and improving fuel quality. Catalytic reforming converts low-octane naphthas into high-octane liquid products called reformates. These reformates are primary blending components for high-octane gasoline. The process also produces hydrogen as a byproduct, which is often used in other refinery units such as hydrodesulfurization and hydrocracking.

Fluid Catalytic Cracking and Hydrocracking

Fluid catalytic cracking (FCC) is one of the most important conversion processes in a modern refinery. The FCC unit breaks down large, heavy hydrocarbon molecules into smaller, more valuable molecules such as gasoline and light diesel oil. The process uses a powdered catalyst that flows through the reactor, allowing for continuous operation and efficient heat transfer. Hydrocracking combines hydrogenation and catalytic cracking to break down heavy oil fractions into lighter products. This process is particularly effective for converting heavy vacuum gas oil into high-quality diesel and jet fuel. Hydrocracking also helps to remove impurities such as sulfur and nitrogen, producing cleaner fuels.

Alkylation and Coking

Alkylation is a process that combines small hydrocarbon molecules, such as isobutane and olefins, to form larger, branched-chain molecules called alkylates. The process improves the volatility and combustion characteristics of the final fuel. Coking is a thermal cracking process that converts heavy residual oil into lighter products and a solid carbon residue called coke. The coke produced can be used as fuel or as a feedstock for steel production. Coking helps to maximize the yield of lighter products from heavy crude oil, making it an essential unit for refineries processing heavier feedstocks. These processes work together to optimize the overall efficiency and product slate of the refinery.

Refinery location and infrastructure

Oil refineries are typically situated near oil depots to facilitate the efficient storage of incoming crude oil feedstock as well as bulk liquid products. This proximity minimizes transportation costs and ensures a steady supply of raw materials for the industrial process plant. The location of these facilities is critical for managing the logistics of both inputs and outputs, including gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefied petroleum gas, and petroleum naphtha. Additionally, some refineries produce petrochemical feedstocks like ethylene and propylene directly by cracking crude oil, further influencing site selection based on downstream market demands.

Infrastructure and Storage

The infrastructure surrounding an oil refinery includes extensive storage capabilities for crude oil and refined products. These depots are essential for buffering against fluctuations in supply and demand, ensuring continuous operation of the refinery. The design and capacity of these storage facilities are tailored to the specific needs of the refinery, accommodating the diverse range of products generated during the refining process. Efficient infrastructure also supports the transportation of these products to various markets, leveraging both land and water routes depending on the geographic location of the refinery.

Safety, environment and worker health

Oil refineries present significant environmental and occupational challenges due to the complex chemical processes involved in transforming crude oil into usable fuels and petrochemicals. The industry manages substantial air and water pollution, while workers face exposure to hazardous substances, extreme heat, and noise. Regulatory frameworks globally aim to mitigate these impacts, though enforcement and technology adoption vary by region.

Environmental Impacts

Refineries are major sources of air emissions, including sulfur dioxide, nitrogen oxides, volatile organic compounds (VOCs), and particulate matter. These emissions contribute to smog formation, acid rain, and respiratory health issues in nearby communities. Water pollution arises from cooling towers, process wastewater, and runoff containing hydrocarbons and heavy metals. Refineries often use large volumes of water for cooling and processing, leading to thermal pollution in nearby water bodies. The storage of crude oil and refined products also poses risks of spills and leaks, which can contaminate soil and groundwater.

Occupational Hazards

Workers in oil refineries are exposed to a variety of occupational hazards. Benzene, toluene, and xylene (BTX) are common aromatic hydrocarbons found in crude oil and refined products. Prolonged exposure to BTX can lead to respiratory issues, neurological effects, and increased cancer risk. Heat stress is a significant concern, especially in distillation columns and furnaces where temperatures can exceed 100°C. Noise pollution from pumps, compressors, and turbines can cause hearing loss if not properly managed. Additionally, the presence of flammable and explosive gases increases the risk of fires and explosions, requiring strict safety protocols and personal protective equipment (PPE).

Regulatory Frameworks

Regulatory frameworks for oil refineries vary by country but generally focus on emission limits, waste management, and worker safety. In the United States, the Environmental Protection Agency (EPA) enforces the Clean Air Act and Clean Water Act, setting standards for refinery emissions and wastewater discharge. The Occupational Safety and Health Administration (OSHA) regulates workplace safety, including exposure limits for chemicals like benzene. In Europe, the Industrial Emissions Directive (IED) sets best available techniques (BAT) for reducing emissions and improving energy efficiency. Regulatory compliance often requires refineries to invest in advanced technologies, such as scrubbers for air pollution control and membrane filtration for water treatment. Despite these efforts, regulatory gaps and enforcement challenges remain, particularly in emerging markets.

Corrosion and maintenance

Corrosion represents a critical operational challenge in oil refineries, directly impacting the efficiency and longevity of the industrial process plant where petroleum is transformed into products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefied petroleum gas and petroleum naphtha. The complex chemical environment within these facilities, where crude oil feedstock is processed, subjects infrastructure to diverse corrosive agents. Petrochemical feedstock like ethylene and propylene, which can be produced directly by cracking crude oil without the need of using refined products of crude oil such as naphtha, introduces additional thermal and chemical stressors that accelerate material degradation.

Material Selection and Infrastructure

The selection of materials for refinery infrastructure is dictated by the specific corrosive nature of the feedstock and the resulting products. The industrial process plant must utilize materials capable of resisting the corrosive effects of sulfur compounds, water, and acidic byproducts inherent in the transformation of petroleum. Proper material selection ensures that the facilities responsible for producing gasoline (petrol), diesel fuel, and other key outputs maintain structural integrity under high-pressure and high-temperature conditions.

Maintenance and Efficiency

Effective maintenance strategies are essential to mitigate the impact of corrosion on the overall efficiency of the refinery. In 2020, the total capacity of global refineries for crude oil was about 101.2 million barrels per day, highlighting the scale at which corrosion management must be executed to prevent significant production losses. Regular inspection and maintenance of the oil production plant components are necessary to ensure that the crude oil feedstock is processed without excessive downtime. The storage facilities, including the oil depot for incoming crude oil feedstock and bulk liquid products, require continuous monitoring to prevent leaks and structural failures caused by corrosive wear. Maintaining the integrity of these systems is crucial for sustaining the production of essential fuels such as heating oil, kerosene, and liquefied petroleum gas.