Oil refining technologies. Oil distillation, primary and secondary oil refining
The essence of oil refining production
The oil refining process can be divided into 3 main stages:
1. Separation of petroleum feedstock into fractions that differ in boiling temperature ranges (primary processing);
2. Processing of the obtained fractions by chemical transformations of the hydrocarbons they contain and the production of components of commercial petroleum products (recycling);
3. Mixing components with the involvement, if necessary, of various additives, to obtain commercial petroleum products with specified quality indicators (commodity production).
The refinery's products include motor and boiler fuels, liquefied gases, different kinds raw materials for petrochemical production, and also, depending on the technological scheme of the enterprise - lubricating, hydraulic and other oils, bitumen, petroleum cokes, paraffins. Based on the set of technological processes, the refinery can produce from 5 to more than 40 items of commercial petroleum products.
Oil refining is a continuous production; the period of production between major overhauls at modern plants is up to 3 years. The functional unit of a refinery is the technological installation- a production facility with a set of equipment that allows the full cycle of a particular technological process to be carried out.
This material briefly describes the main technological processes of fuel production - the production of motor and boiler fuels, as well as coke.
Delivery and reception of oil
In Russia, the main volumes of crude oil supplied for processing are supplied to refineries from production associations via main oil pipelines. Small quantities of oil, as well as gas condensate, are supplied by railway. In oil importing countries with access to the sea, supplies to port refineries are carried out by water transport.
Raw materials received at the plant are supplied to the appropriate containers commodity base(Fig. 1), connected by pipelines to all process units of the refinery. The amount of oil received is determined according to instrument metering data, or by measurements in raw material tanks.
Preparation of oil for refining (electric desalting)
Crude oil contains salts that are highly corrosive technological equipment. To remove them, oil coming from raw material tanks is mixed with water in which the salts are dissolved and supplied to the ELOU - electrical desalination plant(Fig. 2). The desalting process is carried out in electric dehydrators- cylindrical devices with electrodes mounted inside. Under the influence of high voltage current (25 kV or more), the mixture of water and oil (emulsion) is destroyed, water collects at the bottom of the apparatus and is pumped out. For more effective destruction of the emulsion, special substances are introduced into the raw materials - demulsifiers. Process temperature - 100-120°C.
Primary oil refining
Desalted oil from the ELOU is supplied to an atmospheric-vacuum distillation unit, which at Russian refineries is designated by the abbreviation AVT - atmospheric-vacuum tube. This name is due to the fact that the heating of the raw material before dividing it into fractions is carried out in coils tube furnaces(Fig. 6) due to the heat of fuel combustion and the heat of flue gases.
AVT is divided into two blocks - atmospheric and vacuum distillation.
1. Atmospheric distillation
Atmospheric distillation (Fig. 3.4) is intended for selection light oil fractions- gasoline, kerosene and diesel, boiling up to 360°C, the potential yield of which is 45-60% of oil. The remainder of atmospheric distillation is fuel oil.
The process consists of separating oil heated in a furnace into separate fractions into distillation column- a cylindrical vertical apparatus, inside of which there are contact devices (plates), through which vapor moves upward and liquid moves downward. Distillation columns of various sizes and configurations are used in almost all oil refining installations; the number of trays in them varies from 20 to 60. Heat is supplied to the bottom of the column and heat is removed from the top of the column, and therefore the temperature in the apparatus gradually decreases from the bottom to the top. As a result, the gasoline fraction is removed from the top of the column in the form of vapor, and the vapors of the kerosene and diesel fractions are condensed in the corresponding parts of the column and removed, the fuel oil remains liquid and is pumped out from the bottom of the column.
2. Vacuum distillation
Vacuum distillation (Fig. 3,5,6) is intended for selection from fuel oil oil distillates at refineries of fuel-oil profile, or wide oil fraction (vacuum gas oil) at a fuel profile refinery. The remainder of vacuum distillation is tar.
The need to select oil fractions under vacuum is due to the fact that at temperatures above 380°C the thermal decomposition of hydrocarbons begins (cracking), and the boiling point of vacuum gas oil is 520°C or more. Therefore, distillation is carried out at a residual pressure of 40-60 mm Hg. Art., which allows you to reduce maximum temperature in the apparatus up to 360-380°C.
The vacuum in the column is created using appropriate equipment; the key devices are steam or liquid ejectors(Fig. 7).
3. Stabilization and secondary distillation of gasoline
The gasoline fraction obtained in an atmospheric unit contains gases (mainly propane and butane) in a volume exceeding quality requirements and cannot be used either as a component of motor gasoline or as commercial straight-run gasoline. In addition, oil refining processes aimed at increasing the octane number of gasoline and the production of aromatic hydrocarbons use narrow gasoline fractions as raw materials. This explains the inclusion in technological scheme oil refining of this process (Fig. 4), in which liquefied gases are distilled from the gasoline fraction, and it is distilled into 2-5 narrow fractions on the appropriate number of columns.
Primary oil refining products are cooled in heat exchangers, in which heat is transferred to cold raw materials supplied for processing, due to which process fuel is saved, in water and air refrigerators and are taken out of production. A similar heat exchange scheme is used in other refinery units.
Modern primary processing plants are often combined and can include the above processes in various configurations. The capacity of such installations ranges from 3 to 6 million tons of crude oil per year.
Several primary processing units are being built at factories to avoid a complete shutdown of the plant when one of the units is taken out for repairs.
Primary petroleum products
|
Name |
Boiling ranges |
Where is it selected? |
Where is it used? |
|
Reflux stabilization |
Propane, butane, isobutane |
Stabilization block |
Gas fractionation, commercial products, process fuel |
|
Stable straight-run gasoline (naphtha) |
Secondary distillation of gasoline |
Gasoline blending, commercial products |
|
|
Stable light petrol |
Stabilization block |
Isomerization, gasoline blending, commercial products |
|
|
Benzene |
Secondary distillation of gasoline |
Production of corresponding aromatic hydrocarbons |
|
|
Toluene |
Secondary distillation of gasoline |
||
|
Xylene |
Secondary distillation of gasoline |
||
|
Catalytic reforming feedstock |
Secondary distillation of gasoline |
Catalytic reforming |
|
|
Heavy petrol |
Secondary distillation of gasoline |
Mixing kerosene, winter diesel fuel, catalytic reforming |
|
|
Kerosene component |
Atmospheric distillation |
Mixing kerosene and diesel fuels |
|
|
Diesel |
Atmospheric distillation |
Hydrotreating, mixing of diesel fuels, fuel oils |
|
|
Atmospheric distillation (residue) |
Vacuum distillation, hydrocracking, fuel oil mixing |
||
|
Vacuum gas oil |
Vacuum distillation |
Catalytic cracking, hydrocracking, commercial products, fuel oil mixing. |
|
|
Vacuum distillation (residue) |
Coking, hydrocracking, fuel oil mixing. |
**) - k.k. - end of boiling
Photos of primary processing plants of various configurations
 |
 |
 |
| Fig.5. Vacuum distillation unit with a capacity of 1.5 million tons per year at the Turkmenbashi Oil Refinery designed by Uhde. | Rice. 6. Vacuum distillation unit with a capacity of 1.6 million tons per year at the LUKOIL-PNOS refinery. In the foreground is a tubular stove (yellow). | Fig.7. Vacuum-creating equipment from Graham. Three ejectors are visible, into which vapors enter from the top of the column. |
Sergei Pronin
Oil is divided into fractions to obtain petroleum products in two stages, that is, oil distillation goes through primary and secondary processing.
Primary oil refining process
At this stage of distillation, crude oil is preliminary dehydrated and desalted using special equipment to separate salts and other impurities that can cause corrosion of equipment and reduce the quality of refined products. After this, the oil contains only 3-4 mg of salts per liter and no more than 0.1% water. The prepared product is ready for distillation.
Due to the fact that liquid hydrocarbons boil at different temperatures, this property is used during the distillation of oil to separate separate fractions from it at different boiling phases. The distillation of oil at the first oil refineries made it possible to isolate the following fractions depending on temperature: gasoline (boils at 180°C and below), jet fuel (boils at 180-240°C) and diesel fuel (boils at 240-350°C). What remains from oil distillation is fuel oil.
During the distillation process, oil is divided into fractions (components). The result is commercial petroleum products or their components. Oil distillation is initial stage its processing in specialized plants.
When heated, a vapor phase is formed, the composition of which is different from the liquid. The fractions obtained by distilling oil are usually not a pure product, but a mixture of hydrocarbons. Individual hydrocarbons can be isolated only through repeated distillation of petroleum fractions.
Direct distillation of oil is performed
By single evaporation (so-called equilibrium distillation) or simple distillation (fractional distillation);
With and without rectification;
Using a vaporizing agent;
Under vacuum and at atmospheric pressure.
Equilibrium distillation separates oil into fractions less clearly than simple distillation. Moreover, more oil goes into the vapor state at the same temperature in the first case than in the second.
Fractional distillation of oil makes it possible to obtain different for diesel and jet engines), as well as raw materials (benzene, xylenes, ethylbenzene, ethylene, butadiene, propylene), solvents and other products.
Secondary oil refining process
Secondary distillation of oil is carried out by the method of chemical or thermal catalytic splitting of those products that are isolated from it as a result of primary oil distillation. This produces a larger amount of gasoline fractions, as well as raw materials for the production of aromatic hydrocarbons (toluene, benzene and others). The most common secondary oil refining technology is cracking.
Cracking is the process of high-temperature refining of oil and separated fractions to obtain (mainly) products that have a lower content. These include motor fuel, lubricating oils, etc., raw materials for the petrochemical and chemical industries. Cracking occurs with the rupture of C-C bonds and the formation of carbanions or free radicals. C-C bond cleavage occurs simultaneously with dehydrogenation, isomerization, polymerization, and condensation of intermediates and starting materials. The last two processes form a cracking residue, i.e. fraction with a boiling point above 350°C and coke.
Oil distillation by cracking was patented in 1891 by V. G. Shukhov and S. Gavrilov, then these engineering solutions were repeated by W. Barton during the construction of the first industrial installation in the USA.
Cracking is carried out by heating raw materials or exposure to catalysts and high temperature.
Cracking allows you to extract more useful components from fuel oil.
Currently, various types of fuel, petroleum oils, paraffins, bitumens, kerosenes, solvents, soot, lubricants and other petroleum products obtained by processing raw materials can be obtained from crude oil.
Extracted hydrocarbon raw materials ( oil, associated petroleum gas And natural gas) The field goes through a long stage before important and valuable components are isolated from this mixture, from which usable petroleum products will subsequently be obtained.
Oil refining very complicated technological process, which begins with the transportation of petroleum products to oil refineries. Here, oil goes through several stages before becoming a ready-to-use product:
- preparation of oil for primary processing
- primary oil refining (direct distillation)
- oil recycling
- petroleum products purification
Preparing oil for primary processing
Extracted but not processed oil contains various impurities, for example, salt, water, sand, clay, soil particles, and associated gas. The life of the field increases the water content of the oil reservoir and, accordingly, the content of water and other impurities in the produced oil. The presence of mechanical impurities and water interferes with the transportation of oil through oil product pipelines for further processing, causes the formation of deposits in heat exchangers and others, and complicates the process of oil refining.
All extracted oil undergoes a comprehensive purification process, first mechanical, then fine purification.
At this stage, the separation of the extracted raw materials into oil and gas into oil and gas also occurs.
Settling in sealed containers, either cold or heated, removes large amounts of water and solids. For getting high performance During the operation of installations for further oil processing, the latter is subjected to additional dehydration and desalting in special electric desalting plants.
Often, water and oil form a poorly soluble emulsion in which tiny droplets of one liquid are suspended in the other.
There are two types of emulsions:
- hydrophilic emulsion, i.e. oil in water
- hydrophobic emulsion, i.e. water in oil
There are several ways to break emulsions:
- mechanical
- chemical
- electric
Mechanical method in turn is divided into:
- upholding
- centrifugation
The difference in the densities of the emulsion components makes it possible to easily separate water and oil by settling by heating the liquid to 120-160°C under a pressure of 8-15 atmospheres for 2-3 hours. In this case, evaporation of water is not allowed.
The emulsion can also be separated under the action of centrifugal forces in centrifuges when reaching 3500-50000 rpm.
With the chemical method the emulsion is broken by the use of demulsifiers, i.e. surfactants. Demulsifiers have greater activity compared to the active emulsifier, form an emulsion of the opposite type, and dissolve the adsorption film. This method used together with electric.
In electric dehydrator installations with electrical influence On an oil emulsion, water particles combine, and faster separation with oil occurs.
Primary oil refining
Extracted oil is a mixture of naphthenic, paraffinic, aromatic carbohydrates, which have different molecular weights and boiling points, and sulfur, oxygen and nitrogen organic compounds. Primary oil refining consists of separating prepared oil and gases into fractions and groups of hydrocarbons. During distillation, a wide range of petroleum products and intermediates are obtained.
The essence of the process is based on the principle of the difference in boiling temperatures of the components of extracted oil. As a result, the raw material decomposes into fractions - to fuel oil (light oil products) and to tar (oil).
Primary distillation of oil can be carried out with:
- single evaporation
- multiple evaporation
- gradual evaporation
During a single evaporation, the oil is heated in the heater to a predetermined temperature. As it heats up, vapors are formed. When the set temperature is reached, the vapor-liquid mixture enters the evaporator (a cylinder in which steam is separated from the liquid phase).
Process multiple evaporation represents a sequence of single evaporations with a gradual increase in heating temperature.
Distillation gradual evaporation represents a small change in the state of oil with each single evaporation.
The main devices in which oil distillation, or distillation, takes place are tube furnaces, distillation columns and heat exchangers.
Depending on the type of distillation, tube furnaces are divided into atmospheric furnaces AT, vacuum furnaces VT and atmospheric-vacuum tube furnaces AVT. AT installations carry out shallow processing and obtain gasoline, kerosene, diesel fractions and fuel oil. In VT installations, advanced processing of raw materials is carried out and gas oil and oil fractions, tar are obtained, which are subsequently used for the production of lubricating oils, coke, bitumen, etc. In AVT furnaces, two methods of oil distillation are combined.
The process of oil refining by the principle of evaporation occurs in distillation columns. There, the source oil is supplied to a heat exchanger using a pump, heated, and then enters a tubular furnace (fire heater), where it is heated to a given temperature. Next, oil in the form of a vapor-liquid mixture enters the evaporation part of the distillation column. Here the division of the vapor phase and the liquid phase occurs: the steam rises up the column, the liquid flows down.
The above methods of oil refining cannot be used to isolate individual high-purity hydrocarbons from oil fractions, which will subsequently become raw materials for the petrochemical industry to produce benzene, toluene, xylene, etc. To obtain high-purity hydrocarbons, an additional substance is introduced into oil distillation units to increase the difference in the volatility of separated hydrocarbons.
The resulting components after primary oil refining are usually not used as a finished product. At the primary distillation stage, the properties and characteristics of the oil are determined, on which the choice of further processing process to obtain the final product depends.
As a result of primary oil processing, the following main petroleum products are obtained:
- hydrocarbon gas (propane, butane)
- gasoline fraction (boiling point up to 200 degrees)
- kerosene (boiling point 220-275 degrees)
- gas oil or diesel fuel (boiling point 200-400 degrees)
- lubricating oils (boiling point above 300 degrees) residue (fuel oil)
Oil recycling
Depending on the physical and chemical properties oil and the need for the final product, the choice of further method of destructive processing of raw materials is made. Petroleum recycling consists of thermal and catalytic effects on petroleum products obtained by direct distillation. The impact on raw materials, that is, the hydrocarbons contained in oil, changes their nature.
There are options for oil refining:
- fuel
- fuel and oil
- petrochemical
Fuel method processing is used to produce high-quality motor gasoline, winter and summer diesel fuels, jet engine fuels, and boiler fuels. This method uses fewer technological installations. The fuel method is a process that produces motor fuels from heavy petroleum fractions and residues. This type of processing includes catalytic cracking, catalytic reforming, hydrocracking, hydrotreating and other thermal processes.
During fuel and oil processing Along with fuels, lubricating oils and asphalt are produced. This type includes extraction and deasphalting processes.
The greatest variety of petroleum products is obtained as a result petrochemical refining. In this regard, a large number of technological installations are used. As a result of petrochemical processing of raw materials, not only fuels and oils are produced, but also nitrogen fertilizers, synthetic rubber, plastics, synthetic fibers, detergents, fatty acids, phenol, acetone, alcohol, ethers and other chemicals.
Catalytic cracking
Catalytic cracking uses a catalyst to speed up chemical processes, but at the same time without changing the essence of these chemical reactions. The essence of the cracking process, i.e. The splitting reaction consists of passing oils heated to a vapor state through a catalyst.
Reforming
The reforming process is used primarily to produce high-octane gasoline. Only paraffin fractions boiling in the range of 95-205°C can be subjected to this processing.
Types of reforming:
- thermal reforming
- catalytic reforming
During thermal reforming Fractions of primary oil refining are exposed only to high temperatures.
During catalytic reforming the impact on the initial fractions occurs both with temperature and with the help of catalysts.
Hydrocracking and hydrotreating
This processing method consists of obtaining gasoline fractions, jet and diesel fuel, lubricating oils and liquefied gases due to the effect of hydrogen on high-boiling oil fractions under the influence of a catalyst. As a result of hydrocracking, the original oil fractions also undergo hydrotreating.
Hydrotreating involves removing sulfur and other impurities from raw materials. Typically, hydrotreating units are combined with catalytic reforming units, since as a result of the latter, a large number of hydrogen. As a result of purification, the quality of petroleum products increases and equipment corrosion decreases.
Extraction and deasphalting
Extraction process consists of separating a mixture of solid or liquid substances using solvents. The extracted components dissolve well in the solvent used. Next, dewaxing is carried out to reduce the pour point of the oil. The final product is obtained through hydrotreating. This processing method is used to produce diesel fuel and extract aromatic hydrocarbons.
As a result of deasphalting, resinous asphaltene substances are obtained from residual oil distillation products. Subsequently, the deasphalted oil is used to produce bitumen and is used as a raw material for catalytic cracking and hydrocracking.
Coking
To obtain petroleum coke and gas oil fractions from heavy fractions of oil distillation, deasphalting residues, thermal and catalytic cracking, and pyrolysis of gasoline, the coking process is used. This type refining of petroleum products consists of the sequential reactions of cracking, dehydrogenation (release of hydrogen from raw materials), cyclization (formation of a cyclic structure), aromatization (increase in aromatic hydrocarbons in oil), polycondensation (release of by-products such as water, alcohol) and compaction to form a complete "coke pie". Volatile products released during the coking process are subjected to a rectification process to obtain the target fractions and stabilize them.
Isomerization
The isomerization process consists of converting its isomers from the feedstock. Such transformations lead to the production of gasoline with a high octane number.
Alkylation
By introducing alkyne groups into compounds, high-octane gasoline is obtained from hydrocarbon gases.
It should be noted that in the process of oil refining and to obtain the final product, the entire complex of oil, gas and petrochemical technologies is used. The complexity and variety of finished products that can be obtained from the extracted raw materials also determine the diversity of oil refining processes.
Crude oil is the term used to refer to unprocessed oil - the raw material that comes out of the ground as is. Thus, crude oil is a fossil fuel, meaning that it was produced naturally from decaying plants and animals that lived in ancient seas millions of years ago - most of the places where oil is most often found were once seabeds. Depending on the field, crude oil varies in color and consistency: from bright black (wet asphalt) and very viscous, to slightly transparent and almost solid.
The main value and benefit of oil is that it is the starting point for so many different substances, since it contains hydrocarbons. Hydrocarbons are molecules that obviously contain hydrogen and carbon, and differ from each other only in that they can be of different lengths and structures - from straight chains to branched chains with rings.
There are two things that make hydrocarbons interesting to chemists:
- Hydrocarbons contain a lot of potential energy. Much of what is obtained from crude oil, such as gasoline, diesel fuel, paraffin, etc. - is valuable precisely because of this potential energy.
- Hydrocarbons can take many various forms. The smallest hydrocarbon (by number of atoms) is methane (CH4), which is a gas that is lighter than air. Longer chains with 5 or more carbon atoms are in the vast majority of cases liquids. And very long chains are hard, for example, wax or resin. Based on the chemical structure of “cross-linking” hydrocarbon chains, you can get everything from synthetic rubber to nylon and plastic. Hydrocarbon chains are actually very versatile!
The main classes of hydrocarbons in crude oil include:
- Paraffins with the general formula C n H 2n+2 (n is an integer, usually from 1 to 20) with a straight or branched chain structure can represent gases or liquids that already boil at room temperature, depending on the examples of molecules: methane, ethane, propane, butane, isobutane, pentane, hexane.
- Aromatics with the general formula: C 6 H 5 -Y (Y is a large straight molecule that connects to a benzene ring) are ring structures with one or more rings that contain six carbon atoms, with alternating double single bonds between the carbon atoms. Vivid examples of aromatics: benzene and naphthalene.
- Naphthenes or cycloalkanes with the general formula CnH2n (n is an integer, typically from 1 to 20) are ringed structures with one or more rings that contain only simple bonds between carbon atoms. These are, as a rule, liquids: cyclohexane, methylcyclopentane and others.
- Alkenes with the general formula C n H 2n (n is an integer, usually from 1 to 20) are linear or branched chain molecules containing a single carbon-carbon double bond, which can be a liquid or a gas, for example: ethylene, butene, isobutene .
- Alkynes with the general formula: C n H 2n-2 (n is an integer, usually from 1 to 20) are linear or branched chain molecules containing two carbon-carbon double bonds, which can be a liquid or a gas, for example: acetylene, butadienes.
Now that we know the structure of oil, let's see what we can do with it.
How does oil refining work?
The oil refining process begins with a fractional distillation column.
Typical oil refinery
The main problem with crude oil is that it contains hundreds of various types hydrocarbons mixed together. And our job is to separate out the different types of hydrocarbons to get something useful. Luckily, there is a simple way to separate these things, and that's what petroleum refining does.
Different lengths of the hydrocarbon chain have progressively higher boiling points, so that they can be separated by simple distillation at different temperatures. Simply put, by heating oil to a certain temperature, certain chains of hydrocarbons begin to boil, and thus we can separate the “wheat from the chaff.” This is what happens in an oil refinery - in one part of the process the oil is heated and the various chains are boiled off at their respective boiling points. Each different length of chain has its own unique property, making it useful in its own way.
To understand the diversity contained in crude oil and why crude oil refining is so important in our civilization, take a look at next list products obtained from crude oil:
Petroleum gases- used for heating, cooking, making plastics:
- these are small alkanes (1 to 4 carbon atoms)
- widely known by such names as methane, ethane, propane, butane
- boiling range - less than 40 degrees Celsius
- gases often liquefied under pressure
Naphtha or naphtha- an intermediate product that will be further processed to subsequently become gasoline:
- contains from 5 to 9 carbon alkane atoms
- boiling range - from 60 to 100 degrees Celsius
Petrol- motor fuel:
- always a liquid product
- is a mixture of alkanes and cycloalkanes (5 to 12 carbon atoms)
- boiling range - from 40 to 205 degrees Celsius
Kerosene- fuel for jet engines and tractors; starting material for the manufacture of other products:
- liquid
- mixture of alkanes (10 to 18 carbon atoms) and aromatic hydrocarbons
- boiling range - from 175 to 325 degrees Celsius
Diesel distillate- used for diesel fuel and fuel oil; starting material for the manufacture of other products:
- liquid
- alkanes containing 12 or more carbon atoms
- boiling range - from 250 to 350 degrees Celsius
Lubricating oils- used for making motor oil, fat, other lubricants:
- liquid
- long chain structures (from 20 to 50 carbon atoms) alkanes, cycloalkanes, aromatics
- boiling range - from 300 to 370 degrees Celsius
Fuel oil- used for industrial fuel; starting material for the manufacture of other products:
- liquid
- long chain structures (from 20 to 70 carbon atoms) alkanes, cycloalkanes, aromatics
- boiling range - 370 to 600 degrees Celsius
Remains of processed products- coke, asphalt, tar, paraffins; starting material for the manufacture of other products:
- particulate matter
- multiple ring compounds with 70 or more carbon atoms
- boiling range of at least 600 degrees Celsius.
You may have noticed that all of these products have different sizes and boiling ranges. Chemists took advantage of these properties for oil refining. Let's now further find out the details of this fascinating process!
Detailed oil refining process
As mentioned earlier, a barrel of crude oil has a mixture of all kinds of hydrocarbons in it. Oil refining separates us from this whole “company of multiracial representatives” useful material. At the same time, there are the following groups production chemical processes, which, in principle, exist at every oil refinery:
- The oldest and most common way to separate different components (called fractions) from oil is to do so using differences in boiling points. This process is called fractional distillation .
- New methods of using chemical treatment in some of the fractions use the conversion method. Chemical treatment, for example, can break long chains into shorter ones. This allows the refinery to turn diesel into gasoline depending on demand, for example.
- Refineries must also clean the fractions after the fractional distillation process to remove impurities.
- Oil refineries combine different fractions (processed and unprocessed) into mixtures to make the desired products. For example, different mixtures from different chains can create gasolines with different octane numbers.
Petroleum products are sent for short-term storage in special tanks until they are delivered to various markets: gas stations, airports and chemical plants. In addition to creating oil-based products, factories must also take care of the inevitable waste generated to minimize air and water pollution.
Fractional distillation
The different components of petroleum have different sizes, weights and boiling points; so the first step is to separate these components. Because they have different boiling points, they can be separated easily using a process called fractional distillation.
The stages of fractional distillation are as follows:
- You heat a mixture of two or more substances (liquids) with different boiling points to a high temperature. Heating is usually done using high pressure steam to a temperature of around 600 degrees Celsius.
- The mixture boils, producing steam (gases); Most substances pass through in the vapor phase.
- The steam enters the bottom of a long column, which is filled with trays or trays. Trays have many holes or bubble caps (similar to the holey lid on plastic bottle) into them to allow steam to pass through them. They increase the contact time between vapor and liquid in the column and help collect liquids that form at various heights in the column. There is a temperature difference in this column (very hot at the bottom and cooler towards the top).
- Thus, the steam rises in the column.
- As the vapor rises through the plates in the column, it cools.
- When a vaporous substance reaches a height where the temperature in the column is equal to the boiling point of that substance, it will condense to form a liquid. In this case, substances with the lowest boiling points will condense at the highest point in the column, and substances with higher boiling points will condense lower in the column.
- Trays collect various liquid fractions.
- The collected liquid fractions can go to condensers, which cool them further, and then go to storage tanks, or they can go to other areas for further chemical processing
Fractional distillation is useful for separating a mixture of substances with narrow differences in boiling points and is the most important step in the petroleum refining process. The oil refining process begins with a fractional distillation column. Very few of the components will emerge from the fractional distillation column ready for sale to the petroleum products market. Many of them must be chemically treated in order to be converted into other fractions. For example, only 40% of distilled crude oil will become gasoline, however, gasoline is one of the main products produced by oil companies. Instead of constantly distilling into large quantities crude oil, oil companies chemically treat other fractions from the distillation column to produce the same gasoline; and this treatment increases the gasoline yield from each barrel of crude oil.
Chemical transformation
You can convert one faction to another using one of three methods:
- Break large hydrocarbons into smaller ones (cracking)
- Combine small hydrocarbons to make larger ones (unification)
- Rearrange or replace different parts of hydrocarbons to produce desired hydrocarbons (hydrothermal alteration)
Cracking
Cracking takes large hydrocarbons and breaks them into smaller ones. There are several types of cracking:
- Thermal- You heat large hydrocarbons at high temperatures (sometimes also at high pressures) until they disintegrate.
- Steam - heat steam (over 800 degrees Celsius) is used to break ethane, butane and naphtha into ethylene and benzene, which are used to produce chemicals.
- Visbreaking- the residuals from the distillation column are heated to almost 500 degrees Celsius, cooled and quickly burned in the distillation column. This process reduces the viscosity of substances and the amount of heavy oils in them and produces resins.
- Coking- residual substances from the distillation column are heated to temperatures above 450 degrees Celsius, as a result of which heavy almost pure carbon remains (coke); the coke is decoked and sold.
- Catalysis- a catalyst is used to speed up the cracking reaction. Catalysts include zeolite, hydrous aluminum silicate, bauxite and aluminosilicate. Catalytic cracking is when a hot catalyst liquid (538 degrees Celsius) breaks down a heavy substance into diesel oils and gasoline.
- Hydrocracking- similar to catalytic cracking, but uses a different catalyst with lower temperatures, high pressure and hydrogen. This allows heavy oil to be broken down into gasoline and kerosene (jet fuel).
Unification
Sometimes you need to combine small hydrocarbons to make larger ones, a process called unification. The main unification process is catalytic reforming and in this case a catalyst (a mixture of platinum and platinum-rhenium) is used to combine the low weight naphtha into aromatic compounds that are used in creating chemicals and in gasoline blending. A significant byproduct of this reaction is hydrogen gas, which is then either used for hydrocracking or simply sold.
Hydrothermal alteration
Sometimes the molecular structures in one fraction are rearranged to produce another. Typically this is done through a process called alkylation. In alkylation, low molecular weight compounds such as propylene and butylene are mixed in the presence of a catalyst such as hydrofluoric acid or sulfuric acid (a by-product from the removal of impurities from many petroleum products). Alkylation products are high-octane hydrocarbons that are used in gasoline mixtures to increase the octane number.
Final processing (purification) of petroleum products
Distilled and chemically treated petroleum fractions are again processed to remove impurities - mainly organic compounds containing sulfur, nitrogen, oxygen, water, dissolved metals and inorganic salts. Final processing is usually done in the following ways:
- The sulfuric acid column removes unsaturated hydrocarbons (double carbon-carbon-bonds), nitrogen compounds, oxygen compounds and residual solids (tars, asphalt).
- The absorption column is filled with a drying agent to remove water.
- Hydrogen sulfide scrubbers remove sulfur and all sulfur compounds.
Once the fractions are processed, they are cooled and then mixed together to make various products such as:
- Gasoline of various brands, with or without additives.
- Lubricating oils of various brands and types (for example, 10W-40, 5W-30).
- Kerosene of various brands.
- Jet fuel.
- Fuel oil.
- Other chemical substances various grades for the production of plastics and other polymers.
Oil refining methods are divided into primary and secondary. Let's consider the primary methods when oil enters an oil refinery.
Preliminary oil preparation
Rectification
Pre-treated crude oil is separated into hydrocarbon groups (fractions) using primary processing processes - atmospheric distillation and vacuum distillation.
The refining process itself involves the evaporation of crude oil and the distillation of the resulting fractions due to the difference in boiling temperatures. This process is called direct distillation or rectification.
Atmospheric distillation– occurs in a distillation column at atmospheric pressure. As a result, gasoline, kerosene, diesel fractions and fuel oil are obtained.
Vacuum distillation– separation of fuel oil remaining from atmospheric distillation to tar to obtain either a wide distillate fraction (fuel option) or narrow oil fractions (oil option).
Thus, the result of primary oil refining is petroleum products and intermediates for further processing by secondary methods with improvement of their commercial quality.
Oil Refining Processes
Methods recycling Oils can be divided into thermal and catalytic.
Methods used for petroleum recycling can be divided into thermal and catalytic processes.
Visbreaking
Visbreaking is the process of producing boiler fuel from tar and similar residual oil refining products with improved performance properties, characterized by a reduced viscosity level and pour point.
During thermal cracking, an additional volume of light raw materials is produced; also, when using this processing process, it is possible to obtain petroleum products used on equipment used for the production of electrode coke and raw materials, on the basis of which carbon black is obtained. The volume of light oil product obtained is quite low and requires further processing.
The raw material for processing by reforming is straight-run gasoline with an octane number of 80-85 units. This method of oil refining allows you to remove 78-82% of the final product. At the same time, the base gasoline obtained in this way contains a fairly high percentage of aromatic hydrocarbons (50-65%), including up to 7% benzene, which significantly increases the level of soot formation and contributes to an increase in the level of emissions of carcinogenic substances into the atmosphere, as well as contains insufficient amounts of light fractions.
To produce gasoline that meets approved standards, light isoparaffins are used, which are removed from paraffins of normal structure using catalytic isomerization in a hydrogen-containing environment.
The lightest part of straight gasoline, the so-called head, remains as a component of commercial gasoline at oil refineries during the production of reforming feedstock. At the same time, the main share of processed oil is characterized by the presence of a head fraction with a low octane number. Increasing the octane number of the light fraction by 15-20 units is possible by isomerizing it, which makes it possible to use it as a component of commercial gasoline.
Hydrocracking
Hydrocracking is the process of processing fuel oil, vacuum gas oil or deasphalted oil under hydrogen pressure, intended to produce any types of light petroleum products, including motor gasoline, diesel fuel, liquefied gases and other types of light petroleum products. The type of final product depends on the settings and volume of hydrogen used.
By the way, read this article too: Delayed coker
Hydrocracking is also used to produce low-boiling hydrocarbons. In this case, the raw materials are middle distillate fractions and heavy gasoline.
Using the hydrocracking process, only decomposition products can be produced; compaction reactions with this method of processing petroleum products are suppressed due to the influence of hydrogen.
Enterprises specializing in the production of fuel and oil products obtain distillate fractions by separating vacuum gas oil from fractions, and residual oil fractions from tar disphalted oil. Typically, extraction processes are used in the production of oils. At the same time, the conditions necessary for the successful completion of processing processes are different, which is due to the difference chemical composition the final product obtained from oils of various origins.
For normal operation today, oil refineries must meet the following requirements:
– be able to produce a sufficient volume of the final product to fully cover the needs of the region;
– produce products that meet modern high quality standards;
– strive to establish a non-stop oil refining process;
– carry out integrated production of oil and gas industry products;
– hold high level competitiveness;
– meet all standards of technological and environmental safety of production.
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